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 $206.94   6.406%   $220.1966   $220.20   $220.20   $220.20  
  Purchase #2 $55.74   12.219%   $62.5509   $62.55   $62.55   $62.60  
  Purchase #3 $167.43   7.721%   $180.3573   $180.36   $180.35   $180.40  
  Purchase #4 $146.65   13.706%   $166.7498   $166.75   $166.75   $166.70  
  Purchase #5 $111.66   5.682%   $118.0045   $118.00   $118.00   $118.00  
  Purchase #6 $146.52   7.589%   $157.6394   $157.64   $157.65   $157.60  
  Purchase #7 $132.47   11.756%   $148.0432   $148.04   $148.05   $148.00  
  7 purchase totals = $967.41       $1,053.5417   $1,053.54   $1,053.55   $1,053.50