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 $153.69   6.341%   $163.4355   $163.44   $163.45   $163.40  
  Purchase #2 $184.82   11.217%   $205.5513   $205.55   $205.55   $205.60  
  Purchase #3 $238.41   9.338%   $260.6727   $260.67   $260.65   $260.70  
  Purchase #4 $118.36   5.237%   $124.5585   $124.56   $124.55   $124.60  
  Purchase #5 $91.76   4.670%   $96.0452   $96.05   $96.05   $96.00  
  Purchase #6 $199.46   13.764%   $226.9137   $226.91   $226.90   $226.90  
  Purchase #7 $176.76   11.464%   $197.0238   $197.02   $197.00   $197.00  
  7 purchase totals = $1,163.26       $1,274.2007   $1,274.20   $1,274.15   $1,274.20