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 $240.61   4.183%   $250.6747   $250.67   $250.65   $250.70  
  Purchase #2 $49.42   11.837%   $55.2698   $55.27   $55.25   $55.30  
  Purchase #3 $62.26   7.600%   $66.9918   $66.99   $67.00   $67.00  
  Purchase #4 $93.99   12.281%   $105.5329   $105.53   $105.55   $105.50  
  Purchase #5 $157.60   4.594%   $164.8401   $164.84   $164.85   $164.80  
  Purchase #6 $136.37   10.701%   $150.963   $150.96   $150.95   $151.00  
  Purchase #7 $155.61   7.140%   $166.7206   $166.72   $166.70   $166.70  
  7 purchase totals = $895.86       $960.9929   $960.98   $960.95   $961.00