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 $198.81   13.851%   $226.3472   $226.35   $226.35   $226.30  
  Purchase #2 $148.69   12.254%   $166.9105   $166.91   $166.90   $166.90  
  Purchase #3 $31.55   6.758%   $33.6821   $33.68   $33.70   $33.70  
  Purchase #4 $83.43   9.142%   $91.0572   $91.06   $91.05   $91.10  
  Purchase #5 $124.79   13.754%   $141.9536   $141.95   $141.95   $142.00  
  Purchase #6 $243.64   6.801%   $260.21   $260.21   $260.20   $260.20  
  Purchase #7 $28.80   7.646%   $31.002   $31.00   $31.00   $31.00  
  7 purchase totals = $859.71       $951.1626   $951.16   $951.15   $951.20