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 $31.50   4.127%   $32.8   $32.80   $32.80   $32.80  
  Purchase #2 $207.59   11.778%   $232.04   $232.04   $232.05   $232.00  
  Purchase #3 $153.58   8.500%   $166.6343   $166.63   $166.65   $166.60  
  Purchase #4 $29.57   11.463%   $32.9596   $32.96   $32.95   $33.00  
  Purchase #5 $98.31   8.846%   $107.0065   $107.01   $107.00   $107.00  
  Purchase #6 $217.80   5.452%   $229.6745   $229.67   $229.65   $229.70  
  Purchase #7 $210.25   5.485%   $221.7822   $221.78   $221.80   $221.80  
  7 purchase totals = $948.60       $1,022.8971   $1,022.89   $1,022.90   $1,022.90