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 $245.80   8.276%   $266.1424   $266.14   $266.15   $266.10  
  Purchase #2 $59.77   9.762%   $65.6047   $65.60   $65.60   $65.60  
  Purchase #3 $148.88   8.409%   $161.3993   $161.40   $161.40   $161.40  
  Purchase #4 $219.64   8.446%   $238.1908   $238.19   $238.20   $238.20  
  Purchase #5 $154.99   8.480%   $168.1332   $168.13   $168.15   $168.10  
  Purchase #6 $62.33   9.414%   $68.1977   $68.20   $68.20   $68.20  
  Purchase #7 $165.42   6.590%   $176.3212   $176.32   $176.30   $176.30  
  7 purchase totals = $1,056.83       $1,143.9893   $1,143.98   $1,144.00   $1,143.90