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 $31.29   13.289%   $35.4481   $35.45   $35.45   $35.40  
  Purchase #2 $223.71   5.510%   $236.0364   $236.04   $236.05   $236.00  
  Purchase #3 $236.52   12.638%   $266.4114   $266.41   $266.40   $266.40  
  Purchase #4 $26.42   11.124%   $29.359   $29.36   $29.35   $29.40  
  Purchase #5 $110.35   13.122%   $124.8301   $124.83   $124.85   $124.80  
  Purchase #6 $160.84   8.731%   $174.8829   $174.88   $174.90   $174.90  
  Purchase #7 $233.38   6.817%   $249.2895   $249.29   $249.30   $249.30  
  7 purchase totals = $1,022.51       $1,116.2574   $1,116.26   $1,116.30   $1,116.20