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 $24.33   7.270%   $26.0988   $26.10   $26.10   $26.10  
  Purchase #2 $190.57   13.746%   $216.7658   $216.77   $216.75   $216.80  
  Purchase #3 $95.96   8.325%   $103.9487   $103.95   $103.95   $103.90  
  Purchase #4 $84.31   9.662%   $92.456   $92.46   $92.45   $92.50  
  Purchase #5 $197.77   4.469%   $206.6083   $206.61   $206.60   $206.60  
  Purchase #6 $82.75   13.654%   $94.0487   $94.05   $94.05   $94.00  
  Purchase #7 $87.27   7.496%   $93.8118   $93.81   $93.80   $93.80  
  7 purchase totals = $762.96       $833.7381   $833.75   $833.70   $833.70