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 $241.56   10.522%   $266.9769   $266.98   $267.00   $267.00  
  Purchase #2 $45.33   12.283%   $50.8979   $50.90   $50.90   $50.90  
  Purchase #3 $52.95   8.785%   $57.6017   $57.60   $57.60   $57.60  
  Purchase #4 $238.99   6.763%   $255.1529   $255.15   $255.15   $255.20  
  Purchase #5 $45.55   8.785%   $49.5516   $49.55   $49.55   $49.60  
  Purchase #6 $233.64   9.203%   $255.1419   $255.14   $255.15   $255.10  
  Purchase #7 $43.44   6.322%   $46.1863   $46.19   $46.20   $46.20  
  7 purchase totals = $901.46       $981.5092   $981.51   $981.55   $981.60