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 $51.98   12.157%   $58.2992   $58.30   $58.30   $58.30  
  Purchase #2 $92.85   13.365%   $105.2594   $105.26   $105.25   $105.30  
  Purchase #3 $117.43   6.645%   $125.2332   $125.23   $125.25   $125.20  
  Purchase #4 $228.31   12.383%   $256.5816   $256.58   $256.60   $256.60  
  Purchase #5 $84.84   3.144%   $87.5074   $87.51   $87.50   $87.50  
  Purchase #6 $234.64   10.211%   $258.5991   $258.60   $258.60   $258.60  
  Purchase #7 $208.85   11.290%   $232.4292   $232.43   $232.45   $232.40  
  7 purchase totals = $1,018.90       $1,123.9091   $1,123.91   $1,123.95   $1,123.90