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 $46.45   11.252%   $51.6766   $51.68   $51.70   $51.70  
  Purchase #2 $179.71   9.148%   $196.1499   $196.15   $196.15   $196.10  
  Purchase #3 $160.90   13.520%   $182.6537   $182.65   $182.65   $182.70  
  Purchase #4 $184.94   12.657%   $208.3479   $208.35   $208.35   $208.30  
  Purchase #5 $205.75   3.820%   $213.6097   $213.61   $213.60   $213.60  
  Purchase #6 $210.46   9.196%   $229.8139   $229.81   $229.80   $229.80  
  Purchase #7 $74.36   3.303%   $76.8161   $76.82   $76.80   $76.80  
  7 purchase totals = $1,062.57       $1,159.0678   $1,159.07   $1,159.05   $1,159.00