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 $95.74   6.436%   $101.9018   $101.90   $101.90   $101.90  
  Purchase #2 $220.72   8.263%   $238.9581   $238.96   $238.95   $239.00  
  Purchase #3 $42.96   7.474%   $46.1708   $46.17   $46.15   $46.20  
  Purchase #4 $182.75   11.859%   $204.4223   $204.42   $204.40   $204.40  
  Purchase #5 $155.36   10.179%   $171.1741   $171.17   $171.15   $171.20  
  Purchase #6 $246.77   11.809%   $275.9111   $275.91   $275.90   $275.90  
  Purchase #7 $149.76   13.393%   $169.8174   $169.82   $169.80   $169.80  
  7 purchase totals = $1,094.06       $1,208.3556   $1,208.35   $1,208.25   $1,208.40