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 $193.76   4.357%   $202.2021   $202.20   $202.20   $202.20  
  Purchase #2 $191.89   10.463%   $211.9675   $211.97   $211.95   $212.00  
  Purchase #3 $59.52   8.575%   $64.6238   $64.62   $64.60   $64.60  
  Purchase #4 $115.68   12.860%   $130.5564   $130.56   $130.55   $130.60  
  Purchase #5 $146.82   7.252%   $157.4674   $157.47   $157.45   $157.50  
  Purchase #6 $62.64   11.746%   $69.9977   $70.00   $70.00   $70.00  
  Purchase #7 $73.31   8.156%   $79.2892   $79.29   $79.30   $79.30  
  7 purchase totals = $843.62       $916.1041   $916.11   $916.05   $916.20