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 $171.54   4.826%   $179.8185   $179.82   $179.80   $179.80  
  Purchase #2 $169.25   3.492%   $175.1602   $175.16   $175.15   $175.20  
  Purchase #3 $64.53   13.595%   $73.3029   $73.30   $73.30   $73.30  
  Purchase #4 $236.69   12.182%   $265.5236   $265.52   $265.50   $265.50  
  Purchase #5 $204.62   10.600%   $226.3097   $226.31   $226.30   $226.30  
  Purchase #6 $111.53   6.705%   $119.0081   $119.01   $119.00   $119.00  
  Purchase #7 $105.46   13.248%   $119.4313   $119.43   $119.45   $119.40  
  7 purchase totals = $1,063.62       $1,158.5543   $1,158.55   $1,158.50   $1,158.50