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 $92.94   6.872%   $99.3268   $99.33   $99.35   $99.30  
  Purchase #2 $158.74   9.396%   $173.6552   $173.66   $173.65   $173.70  
  Purchase #3 $223.54   6.826%   $238.7988   $238.80   $238.80   $238.80  
  Purchase #4 $109.77   11.571%   $122.4715   $122.47   $122.45   $122.50  
  Purchase #5 $59.87   12.318%   $67.2448   $67.24   $67.25   $67.20  
  Purchase #6 $79.68   8.297%   $86.291   $86.29   $86.30   $86.30  
  Purchase #7 $229.40   11.152%   $254.9827   $254.98   $255.00   $255.00  
  7 purchase totals = $953.94       $1,042.7708   $1,042.77   $1,042.80   $1,042.80