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 $48.52   7.133%   $51.9809   $51.98   $52.00   $52.00  
  Purchase #2 $218.65   6.260%   $232.3375   $232.34   $232.35   $232.30  
  Purchase #3 $13.52   10.863%   $14.9887   $14.99   $15.00   $15.00  
  Purchase #4 $92.90   13.389%   $105.3384   $105.34   $105.35   $105.30  
  Purchase #5 $222.62   6.818%   $237.7982   $237.80   $237.80   $237.80  
  Purchase #6 $169.89   5.139%   $178.6206   $178.62   $178.60   $178.60  
  Purchase #7 $191.38   5.219%   $201.3681   $201.37   $201.35   $201.40  
  7 purchase totals = $957.48       $1,022.4324   $1,022.44   $1,022.45   $1,022.40