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 $53.52   12.156%   $60.0259   $60.03   $60.05   $60.00  
  Purchase #2 $67.51   10.631%   $74.687   $74.69   $74.70   $74.70  
  Purchase #3 $98.36   9.217%   $107.4258   $107.43   $107.45   $107.40  
  Purchase #4 $204.79   9.376%   $223.9911   $223.99   $224.00   $224.00  
  Purchase #5 $54.42   12.823%   $61.3983   $61.40   $61.40   $61.40  
  Purchase #6 $112.37   3.729%   $116.5603   $116.56   $116.55   $116.60  
  Purchase #7 $195.45   3.674%   $202.6308   $202.63   $202.65   $202.60  
  7 purchase totals = $786.42       $846.7192   $846.73   $846.80   $846.70