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 $218.58   10.572%   $241.6883   $241.69   $241.70   $241.70  
  Purchase #2 $162.78   12.129%   $182.5236   $182.52   $182.50   $182.50  
  Purchase #3 $144.67   3.711%   $150.0387   $150.04   $150.05   $150.00  
  Purchase #4 $218.44   7.517%   $234.8601   $234.86   $234.85   $234.90  
  Purchase #5 $47.57   5.451%   $50.163   $50.16   $50.15   $50.20  
  Purchase #6 $24.60   4.207%   $25.6349   $25.63   $25.65   $25.60  
  Purchase #7 $126.33   6.868%   $135.0063   $135.01   $135.00   $135.00  
  7 purchase totals = $942.97       $1,019.9149   $1,019.91   $1,019.90   $1,019.90