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 $29.26   13.830%   $33.3067   $33.31   $33.30   $33.30  
  Purchase #2 $88.56   9.591%   $97.0538   $97.05   $97.05   $97.10  
  Purchase #3 $22.90   8.236%   $24.786   $24.79   $24.80   $24.80  
  Purchase #4 $128.88   8.577%   $139.934   $139.93   $139.95   $139.90  
  Purchase #5 $213.49   5.689%   $225.6354   $225.64   $225.65   $225.60  
  Purchase #6 $206.73   9.173%   $225.6933   $225.69   $225.70   $225.70  
  Purchase #7 $65.42   5.146%   $68.7865   $68.79   $68.80   $68.80  
  7 purchase totals = $755.24       $815.1957   $815.20   $815.25   $815.20