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 $151.76   9.569%   $166.2819   $166.28   $166.30   $166.30  
  Purchase #2 $209.51   12.132%   $234.9278   $234.93   $234.95   $234.90  
  Purchase #3 $19.37   5.691%   $20.4723   $20.47   $20.45   $20.50  
  Purchase #4 $131.52   11.578%   $146.7474   $146.75   $146.75   $146.70  
  Purchase #5 $88.92   5.484%   $93.7964   $93.80   $93.80   $93.80  
  Purchase #6 $207.45   8.192%   $224.4443   $224.44   $224.45   $224.40  
  Purchase #7 $180.39   5.170%   $189.7162   $189.72   $189.70   $189.70  
  7 purchase totals = $988.92       $1,076.3863   $1,076.39   $1,076.40   $1,076.30