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 $65.89   12.607%   $74.1968   $74.20   $74.20   $74.20  
  Purchase #2 $70.92   11.423%   $79.0212   $79.02   $79.00   $79.00  
  Purchase #3 $159.32   13.855%   $181.3938   $181.39   $181.40   $181.40  
  Purchase #4 $59.74   8.472%   $64.8012   $64.80   $64.80   $64.80  
  Purchase #5 $187.51   10.115%   $206.4766   $206.48   $206.50   $206.50  
  Purchase #6 $52.25   12.544%   $58.8042   $58.80   $58.80   $58.80  
  Purchase #7 $183.62   12.592%   $206.7414   $206.74   $206.75   $206.70  
  7 purchase totals = $779.25       $871.4352   $871.43   $871.45   $871.40