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 $105.53   12.756%   $118.9914   $118.99   $119.00   $119.00  
  Purchase #2 $152.62   7.249%   $163.6834   $163.68   $163.70   $163.70  
  Purchase #3 $65.91   12.523%   $74.1639   $74.16   $74.15   $74.20  
  Purchase #4 $217.72   5.601%   $229.9145   $229.91   $229.90   $229.90  
  Purchase #5 $127.93   7.415%   $137.416   $137.42   $137.40   $137.40  
  Purchase #6 $19.55   6.415%   $20.8041   $20.80   $20.80   $20.80  
  Purchase #7 $218.79   5.821%   $231.5258   $231.53   $231.55   $231.50  
  7 purchase totals = $908.05       $976.4991   $976.49   $976.50   $976.50