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 $58.49   11.122%   $64.9953   $65.00   $65.00   $65.00  
  Purchase #2 $42.43   7.430%   $45.5825   $45.58   $45.60   $45.60  
  Purchase #3 $202.30   3.673%   $209.7305   $209.73   $209.75   $209.70  
  Purchase #4 $188.49   12.353%   $211.7742   $211.77   $211.75   $211.80  
  Purchase #5 $166.70   9.814%   $183.0599   $183.06   $183.05   $183.10  
  Purchase #6 $5.33   6.424%   $5.6724   $5.67   $5.65   $5.70  
  Purchase #7 $215.33   5.220%   $226.5702   $226.57   $226.55   $226.60  
  7 purchase totals = $879.07       $947.3850   $947.38   $947.35   $947.50