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 $239.83   5.744%   $253.6058   $253.61   $253.60   $253.60  
  Purchase #2 $95.73   7.565%   $102.972   $102.97   $102.95   $103.00  
  Purchase #3 $152.52   5.837%   $161.4226   $161.42   $161.40   $161.40  
  Purchase #4 $168.94   10.151%   $186.0891   $186.09   $186.10   $186.10  
  Purchase #5 $218.89   12.705%   $246.7   $246.70   $246.70   $246.70  
  Purchase #6 $95.84   12.642%   $107.9561   $107.96   $107.95   $108.00  
  Purchase #7 $91.68   6.651%   $97.7776   $97.78   $97.80   $97.80  
  7 purchase totals = $1,063.43       $1,156.5232   $1,156.53   $1,156.50   $1,156.60