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 $186.75   9.425%   $204.3512   $204.35   $204.35   $204.40  
  Purchase #2 $121.68   10.288%   $134.1984   $134.20   $134.20   $134.20  
  Purchase #3 $231.39   12.690%   $260.7534   $260.75   $260.75   $260.80  
  Purchase #4 $36.96   8.358%   $40.0491   $40.05   $40.05   $40.00  
  Purchase #5 $48.92   13.252%   $55.4029   $55.40   $55.40   $55.40  
  Purchase #6 $189.49   8.509%   $205.6137   $205.61   $205.60   $205.60  
  Purchase #7 $161.53   10.591%   $178.6376   $178.64   $178.65   $178.60  
  7 purchase totals = $976.72       $1,079.0063   $1,079.00   $1,079.00   $1,079.00