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 $60.86   8.623%   $66.108   $66.11   $66.10   $66.10  
  Purchase #2 $47.68   7.696%   $51.3495   $51.35   $51.35   $51.30  
  Purchase #3 $73.41   13.471%   $83.2991   $83.30   $83.30   $83.30  
  Purchase #4 $240.26   8.220%   $260.0094   $260.01   $260.00   $260.00  
  Purchase #5 $138.55   7.621%   $149.1089   $149.11   $149.10   $149.10  
  Purchase #6 $200.33   13.281%   $226.9358   $226.94   $226.95   $226.90  
  Purchase #7 $227.73   9.219%   $248.7244   $248.72   $248.70   $248.70  
  7 purchase totals = $988.82       $1,085.5351   $1,085.54   $1,085.50   $1,085.40