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 $116.46   6.301%   $123.7981   $123.80   $123.80   $123.80  
  Purchase #2 $61.94   13.576%   $70.349   $70.35   $70.35   $70.30  
  Purchase #3 $23.37   13.867%   $26.6107   $26.61   $26.60   $26.60  
  Purchase #4 $94.45   7.603%   $101.631   $101.63   $101.65   $101.60  
  Purchase #5 $157.57   7.455%   $169.3168   $169.32   $169.30   $169.30  
  Purchase #6 $214.89   4.155%   $223.8187   $223.82   $223.80   $223.80  
  Purchase #7 $41.79   5.275%   $43.9944   $43.99   $44.00   $44.00  
  7 purchase totals = $710.47       $759.5187   $759.52   $759.50   $759.40