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 $76.82   10.214%   $84.6664   $84.67   $84.65   $84.70  
  Purchase #2 $94.46   9.415%   $103.3534   $103.35   $103.35   $103.40  
  Purchase #3 $244.96   10.382%   $270.3917   $270.39   $270.40   $270.40  
  Purchase #4 $91.60   4.476%   $95.7   $95.70   $95.70   $95.70  
  Purchase #5 $25.84   5.256%   $27.1982   $27.20   $27.20   $27.20  
  Purchase #6 $49.68   5.514%   $52.4194   $52.42   $52.40   $52.40  
  Purchase #7 $42.83   13.464%   $48.5966   $48.60   $48.60   $48.60  
  7 purchase totals = $626.19       $682.3257   $682.33   $682.30   $682.40