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 $148.81   11.392%   $165.7624   $165.76   $165.75   $165.80  
  Purchase #2 $93.34   5.467%   $98.4429   $98.44   $98.45   $98.40  
  Purchase #3 $121.35   8.426%   $131.575   $131.58   $131.60   $131.60  
  Purchase #4 $7.45   9.753%   $8.1766   $8.18   $8.20   $8.20  
  Purchase #5 $210.78   10.384%   $232.6674   $232.67   $232.65   $232.70  
  Purchase #6 $109.38   11.710%   $122.1884   $122.19   $122.20   $122.20  
  Purchase #7 $48.95   12.292%   $54.9669   $54.97   $54.95   $55.00  
  7 purchase totals = $740.06       $813.7796   $813.79   $813.80   $813.90