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 $131.30   12.498%   $147.7099   $147.71   $147.70   $147.70  
  Purchase #2 $161.48   10.737%   $178.8181   $178.82   $178.80   $178.80  
  Purchase #3 $195.29   11.417%   $217.5863   $217.59   $217.60   $217.60  
  Purchase #4 $144.92   4.388%   $151.2791   $151.28   $151.30   $151.30  
  Purchase #5 $64.65   3.539%   $66.938   $66.94   $66.95   $66.90  
  Purchase #6 $28.52   9.769%   $31.3061   $31.31   $31.30   $31.30  
  Purchase #7 $7.78   5.469%   $8.2055   $8.21   $8.20   $8.20  
  7 purchase totals = $733.94       $801.8430   $801.86   $801.85   $801.80