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 $52.93   7.571%   $56.9373   $56.94   $56.95   $56.90  
  Purchase #2 $56.38   11.274%   $62.7363   $62.74   $62.75   $62.70  
  Purchase #3 $125.31   5.630%   $132.365   $132.37   $132.35   $132.40  
  Purchase #4 $202.25   9.658%   $221.7833   $221.78   $221.80   $221.80  
  Purchase #5 $169.50   11.531%   $189.045   $189.05   $189.05   $189.00  
  Purchase #6 $203.90   9.270%   $222.8015   $222.80   $222.80   $222.80  
  Purchase #7 $130.42   3.871%   $135.4686   $135.47   $135.45   $135.50  
  7 purchase totals = $940.69       $1,021.1370   $1,021.15   $1,021.15   $1,021.10