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 $203.29   11.155%   $225.967   $225.97   $225.95   $226.00  
  Purchase #2 $24.79   13.221%   $28.0675   $28.07   $28.05   $28.10  
  Purchase #3 $219.25   13.569%   $249   $249.00   $249.00   $249.00  
  Purchase #4 $28.65   8.115%   $30.9749   $30.97   $30.95   $31.00  
  Purchase #5 $73.84   11.160%   $82.0805   $82.08   $82.10   $82.10  
  Purchase #6 $61.55   5.404%   $64.8762   $64.88   $64.90   $64.90  
  Purchase #7 $195.85   5.410%   $206.4455   $206.45   $206.45   $206.40  
  7 purchase totals = $807.22       $887.4116   $887.42   $887.40   $887.50