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 $42.26   10.761%   $46.8076   $46.81   $46.80   $46.80  
  Purchase #2 $163.50   11.105%   $181.6567   $181.66   $181.65   $181.70  
  Purchase #3 $126.74   3.507%   $131.1848   $131.18   $131.20   $131.20  
  Purchase #4 $71.90   8.820%   $78.2416   $78.24   $78.25   $78.20  
  Purchase #5 $129.84   6.627%   $138.4445   $138.44   $138.45   $138.40  
  Purchase #6 $168.45   3.715%   $174.7079   $174.71   $174.70   $174.70  
  Purchase #7 $15.55   3.791%   $16.1395   $16.14   $16.15   $16.10  
  7 purchase totals = $718.24       $767.1826   $767.18   $767.20   $767.10