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 $179.70   13.406%   $203.7906   $203.79   $203.80   $203.80  
  Purchase #2 $97.46   13.401%   $110.5206   $110.52   $110.50   $110.50  
  Purchase #3 $61.65   10.230%   $67.9568   $67.96   $67.95   $68.00  
  Purchase #4 $102.25   10.164%   $112.6427   $112.64   $112.65   $112.60  
  Purchase #5 $123.27   9.359%   $134.8068   $134.81   $134.80   $134.80  
  Purchase #6 $53.59   12.684%   $60.3874   $60.39   $60.40   $60.40  
  Purchase #7 $55.84   10.824%   $61.8841   $61.88   $61.90   $61.90  
  7 purchase totals = $673.76       $751.9890   $751.99   $752.00   $752.00