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 $181.76   6.580%   $193.7198   $193.72   $193.70   $193.70  
  Purchase #2 $65.91   4.562%   $68.9168   $68.92   $68.90   $68.90  
  Purchase #3 $244.45   10.697%   $270.5988   $270.60   $270.60   $270.60  
  Purchase #4 $121.99   11.405%   $135.903   $135.90   $135.90   $135.90  
  Purchase #5 $98.94   13.712%   $112.5067   $112.51   $112.50   $112.50  
  Purchase #6 $184.26   11.423%   $205.308   $205.31   $205.30   $205.30  
  Purchase #7 $157.55   11.464%   $175.6115   $175.61   $175.60   $175.60  
  7 purchase totals = $1,054.86       $1,162.5646   $1,162.57   $1,162.50   $1,162.50