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 $52.91   9.802%   $58.0962   $58.10   $58.10   $58.10  
  Purchase #2 $113.79   8.351%   $123.2926   $123.29   $123.30   $123.30  
  Purchase #3 $228.25   10.727%   $252.7344   $252.73   $252.75   $252.70  
  Purchase #4 $219.69   12.603%   $247.3775   $247.38   $247.40   $247.40  
  Purchase #5 $31.27   3.316%   $32.3069   $32.31   $32.30   $32.30  
  Purchase #6 $188.84   8.752%   $205.3673   $205.37   $205.35   $205.40  
  Purchase #7 $60.85   5.693%   $64.3142   $64.31   $64.30   $64.30  
  7 purchase totals = $895.60       $983.4891   $983.49   $983.50   $983.50