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 $48.26   8.331%   $52.2805   $52.28   $52.30   $52.30  
  Purchase #2 $227.49   13.860%   $259.0201   $259.02   $259.00   $259.00  
  Purchase #3 $72.80   10.490%   $80.4367   $80.44   $80.45   $80.40  
  Purchase #4 $79.53   11.286%   $88.5058   $88.51   $88.50   $88.50  
  Purchase #5 $156.76   10.597%   $173.3719   $173.37   $173.35   $173.40  
  Purchase #6 $182.90   13.152%   $206.955   $206.96   $206.95   $207.00  
  Purchase #7 $63.56   7.700%   $68.4541   $68.45   $68.45   $68.50  
  7 purchase totals = $831.30       $929.0241   $929.03   $929.00   $929.10