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 $197.83   10.323%   $218.252   $218.25   $218.25   $218.30  
  Purchase #2 $51.80   13.488%   $58.7868   $58.79   $58.80   $58.80  
  Purchase #3 $142.84   4.559%   $149.3521   $149.35   $149.35   $149.40  
  Purchase #4 $80.65   9.641%   $88.4255   $88.43   $88.45   $88.40  
  Purchase #5 $186.65   12.352%   $209.705   $209.71   $209.70   $209.70  
  Purchase #6 $90.58   8.264%   $98.0655   $98.07   $98.05   $98.10  
  Purchase #7 $194.49   8.504%   $211.0294   $211.03   $211.05   $211.00  
  7 purchase totals = $944.84       $1,033.6163   $1,033.63   $1,033.65   $1,033.70