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 $87.27   6.322%   $92.7872   $92.79   $92.80   $92.80  
  Purchase #2 $199.54   4.188%   $207.8967   $207.90   $207.90   $207.90  
  Purchase #3 $220.48   7.199%   $236.3524   $236.35   $236.35   $236.40  
  Purchase #4 $211.59   13.720%   $240.6201   $240.62   $240.60   $240.60  
  Purchase #5 $46.26   7.197%   $49.5893   $49.59   $49.60   $49.60  
  Purchase #6 $163.66   6.351%   $174.054   $174.05   $174.05   $174.10  
  Purchase #7 $59.53   3.469%   $61.5951   $61.60   $61.60   $61.60  
  7 purchase totals = $988.33       $1,062.8948   $1,062.90   $1,062.90   $1,063.00