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 $142.82   6.511%   $152.119   $152.12   $152.10   $152.10  
  Purchase #2 $140.48   5.346%   $147.9901   $147.99   $148.00   $148.00  
  Purchase #3 $48.98   6.122%   $51.9786   $51.98   $52.00   $52.00  
  Purchase #4 $155.81   5.404%   $164.23   $164.23   $164.25   $164.20  
  Purchase #5 $23.96   11.735%   $26.7717   $26.77   $26.75   $26.80  
  Purchase #6 $62.46   4.736%   $65.4181   $65.42   $65.40   $65.40  
  Purchase #7 $13.98   9.424%   $15.2975   $15.30   $15.30   $15.30  
  7 purchase totals = $588.49       $623.8050   $623.81   $623.80   $623.80