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 $146.45   13.428%   $166.1153   $166.12   $166.10   $166.10  
  Purchase #2 $167.63   11.335%   $186.6309   $186.63   $186.65   $186.60  
  Purchase #3 $62.35   5.447%   $65.7462   $65.75   $65.75   $65.70  
  Purchase #4 $11.78   3.811%   $12.2289   $12.23   $12.25   $12.20  
  Purchase #5 $112.47   12.196%   $126.1868   $126.19   $126.20   $126.20  
  Purchase #6 $203.96   9.117%   $222.555   $222.56   $222.55   $222.60  
  Purchase #7 $145.77   10.216%   $160.6619   $160.66   $160.65   $160.70  
  7 purchase totals = $850.41       $940.1250   $940.14   $940.15   $940.10