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 $49.27   13.585%   $55.9633   $55.96   $55.95   $56.00  
  Purchase #2 $226.88   10.713%   $251.1857   $251.19   $251.20   $251.20  
  Purchase #3 $30.55   11.530%   $34.0724   $34.07   $34.05   $34.10  
  Purchase #4 $26.36   8.757%   $28.6683   $28.67   $28.65   $28.70  
  Purchase #5 $222.95   3.874%   $231.5871   $231.59   $231.60   $231.60  
  Purchase #6 $44.42   11.473%   $49.5163   $49.52   $49.50   $49.50  
  Purchase #7 $160.53   8.348%   $173.931   $173.93   $173.95   $173.90  
  7 purchase totals = $760.96       $824.9241   $824.93   $824.90   $825.00