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 $218.56   11.659%   $244.0419   $244.04   $244.05   $244.00  
  Purchase #2 $167.65   7.382%   $180.0259   $180.03   $180.05   $180.00  
  Purchase #3 $35.32   12.400%   $39.6997   $39.70   $39.70   $39.70  
  Purchase #4 $88.43   3.263%   $91.3155   $91.32   $91.30   $91.30  
  Purchase #5 $59.47   13.672%   $67.6007   $67.60   $67.60   $67.60  
  Purchase #6 $92.63   7.271%   $99.3651   $99.37   $99.35   $99.40  
  Purchase #7 $111.99   6.278%   $119.0207   $119.02   $119.00   $119.00  
  7 purchase totals = $774.05       $841.0695   $841.08   $841.05   $841.00