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 $116.65   6.740%   $124.5122   $124.51   $124.50   $124.50  
  Purchase #2 $193.71   9.654%   $212.4108   $212.41   $212.40   $212.40  
  Purchase #3 $132.76   4.283%   $138.4461   $138.45   $138.45   $138.40  
  Purchase #4 $68.95   6.797%   $73.6365   $73.64   $73.65   $73.60  
  Purchase #5 $129.40   7.214%   $138.7349   $138.73   $138.75   $138.70  
  Purchase #6 $119.45   6.672%   $127.4197   $127.42   $127.40   $127.40  
  Purchase #7 $112.31   12.284%   $126.1062   $126.11   $126.10   $126.10  
  7 purchase totals = $873.23       $941.2664   $941.27   $941.25   $941.10