Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.53   4.520%   $124.9328   $124.93   $124.95   $124.90  
  Purchase #2 $148.26   11.850%   $165.8288   $165.83   $165.85   $165.80  
  Purchase #3 $170.48   11.195%   $189.5652   $189.57   $189.55   $189.60  
  Purchase #4 $229.97   12.487%   $258.6864   $258.69   $258.70   $258.70  
  Purchase #5 $212.29   13.781%   $241.5457   $241.55   $241.55   $241.50  
  Purchase #6 $112.86   13.691%   $128.3117   $128.31   $128.30   $128.30  
  Purchase #7 $59.94   11.859%   $67.0483   $67.05   $67.05   $67.00  
  7 purchase totals = $1,053.33       $1,175.9189   $1,175.93   $1,175.95   $1,175.80