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 $223.67   4.849%   $234.5158   $234.52   $234.50   $234.50  
  Purchase #2 $56.94   10.396%   $62.8595   $62.86   $62.85   $62.90  
  Purchase #3 $37.95   13.220%   $42.967   $42.97   $42.95   $43.00  
  Purchase #4 $60.77   7.424%   $65.2816   $65.28   $65.30   $65.30  
  Purchase #5 $117.71   4.139%   $122.582   $122.58   $122.60   $122.60  
  Purchase #6 $103.44   3.283%   $106.8359   $106.84   $106.85   $106.80  
  Purchase #7 $180.97   4.714%   $189.5009   $189.50   $189.50   $189.50  
  7 purchase totals = $781.45       $824.5427   $824.55   $824.55   $824.60