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 $66.86   8.818%   $72.7557   $72.76   $72.75   $72.80  
  Purchase #2 $149.54   11.814%   $167.2067   $167.21   $167.20   $167.20  
  Purchase #3 $236.40   7.112%   $253.2128   $253.21   $253.20   $253.20  
  Purchase #4 $190.65   6.460%   $202.966   $202.97   $202.95   $203.00  
  Purchase #5 $229.44   11.743%   $256.3831   $256.38   $256.40   $256.40  
  Purchase #6 $55.52   3.447%   $57.4338   $57.43   $57.45   $57.40  
  Purchase #7 $11.45   4.607%   $11.9775   $11.98   $12.00   $12.00  
  7 purchase totals = $939.86       $1,021.9356   $1,021.94   $1,021.95   $1,022.00