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 $45.73   10.809%   $50.673   $50.67   $50.65   $50.70  
  Purchase #2 $249.98   7.781%   $269.4309   $269.43   $269.45   $269.40  
  Purchase #3 $84.80   8.564%   $92.0623   $92.06   $92.05   $92.10  
  Purchase #4 $52.96   3.560%   $54.8454   $54.85   $54.85   $54.80  
  Purchase #5 $119.60   4.708%   $125.2308   $125.23   $125.25   $125.20  
  Purchase #6 $16.66   8.113%   $18.0116   $18.01   $18.00   $18.00  
  Purchase #7 $236.58   11.379%   $263.5004   $263.50   $263.50   $263.50  
  7 purchase totals = $806.31       $873.7544   $873.75   $873.75   $873.70