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 $77.71   7.487%   $83.5281   $83.53   $83.55   $83.50  
  Purchase #2 $208.75   13.697%   $237.3425   $237.34   $237.35   $237.30  
  Purchase #3 $83.37   5.121%   $87.6394   $87.64   $87.65   $87.60  
  Purchase #4 $150.47   10.273%   $165.9278   $165.93   $165.95   $165.90  
  Purchase #5 $127.95   13.410%   $145.1081   $145.11   $145.10   $145.10  
  Purchase #6 $178.62   13.612%   $202.9338   $202.93   $202.95   $202.90  
  Purchase #7 $125.68   5.408%   $132.4768   $132.48   $132.50   $132.50  
  7 purchase totals = $952.55       $1,054.9565   $1,054.96   $1,055.05   $1,054.80