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 $7.50   3.109%   $7.7332   $7.73   $7.75   $7.70  
  Purchase #2 $111.44   5.155%   $117.1847   $117.18   $117.20   $117.20  
  Purchase #3 $82.84   9.111%   $90.3876   $90.39   $90.40   $90.40  
  Purchase #4 $224.47   8.249%   $242.9865   $242.99   $243.00   $243.00  
  Purchase #5 $43.38   7.121%   $46.4691   $46.47   $46.45   $46.50  
  Purchase #6 $200.54   12.796%   $226.2011   $226.20   $226.20   $226.20  
  Purchase #7 $145.69   3.129%   $150.2486   $150.25   $150.25   $150.20  
  7 purchase totals = $815.86       $881.2108   $881.21   $881.25   $881.20