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 $48.26   13.605%   $54.8258   $54.83   $54.85   $54.80  
  Purchase #2 $237.86   6.646%   $253.6682   $253.67   $253.65   $253.70  
  Purchase #3 $149.92   8.393%   $162.5028   $162.50   $162.50   $162.50  
  Purchase #4 $151.89   13.485%   $172.3724   $172.37   $172.35   $172.40  
  Purchase #5 $191.82   9.472%   $209.9892   $209.99   $210.00   $210.00  
  Purchase #6 $10.91   4.843%   $11.4384   $11.44   $11.45   $11.40  
  Purchase #7 $189.99   6.797%   $202.9036   $202.90   $202.90   $202.90  
  7 purchase totals = $980.65       $1,067.7004   $1,067.70   $1,067.70   $1,067.70