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 $44.46   9.499%   $48.6833   $48.68   $48.70   $48.70  
  Purchase #2 $53.76   7.816%   $57.9619   $57.96   $57.95   $58.00  
  Purchase #3 $5.41   6.554%   $5.7646   $5.76   $5.75   $5.80  
  Purchase #4 $68.28   11.384%   $76.053   $76.05   $76.05   $76.10  
  Purchase #5 $141.84   13.468%   $160.943   $160.94   $160.95   $160.90  
  Purchase #6 $219.78   9.636%   $240.958   $240.96   $240.95   $241.00  
  Purchase #7 $216.67   9.167%   $236.5321   $236.53   $236.55   $236.50  
  7 purchase totals = $750.20       $826.8959   $826.88   $826.90   $827.00