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 $249.89   5.826%   $264.4486   $264.45   $264.45   $264.40  
  Purchase #2 $187.34   7.640%   $201.6528   $201.65   $201.65   $201.70  
  Purchase #3 $94.52   8.116%   $102.1912   $102.19   $102.20   $102.20  
  Purchase #4 $65.61   9.159%   $71.6192   $71.62   $71.60   $71.60  
  Purchase #5 $28.97   11.191%   $32.212   $32.21   $32.20   $32.20  
  Purchase #6 $241.80   13.682%   $274.8831   $274.88   $274.90   $274.90  
  Purchase #7 $234.80   12.319%   $263.725   $263.73   $263.75   $263.70  
  7 purchase totals = $1,102.93       $1,210.7319   $1,210.73   $1,210.75   $1,210.70