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 $204.36   5.682%   $215.9717   $215.97   $215.95   $216.00  
  Purchase #2 $56.69   9.185%   $61.897   $61.90   $61.90   $61.90  
  Purchase #3 $166.44   8.468%   $180.5341   $180.53   $180.55   $180.50  
  Purchase #4 $135.82   4.258%   $141.6032   $141.60   $141.60   $141.60  
  Purchase #5 $192.78   6.186%   $204.7054   $204.71   $204.70   $204.70  
  Purchase #6 $26.70   7.826%   $28.7895   $28.79   $28.80   $28.80  
  Purchase #7 $41.36   11.257%   $46.0159   $46.02   $46.00   $46.00  
  7 purchase totals = $824.15       $879.5168   $879.52   $879.50   $879.50