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 $147.25   11.389%   $164.0203   $164.02   $164.00   $164.00  
  Purchase #2 $124.49   7.567%   $133.9102   $133.91   $133.90   $133.90  
  Purchase #3 $56.48   12.707%   $63.6569   $63.66   $63.65   $63.70  
  Purchase #4 $192.98   6.366%   $205.2651   $205.27   $205.25   $205.30  
  Purchase #5 $93.88   9.673%   $102.961   $102.96   $102.95   $103.00  
  Purchase #6 $123.85   13.814%   $140.9586   $140.96   $140.95   $141.00  
  Purchase #7 $112.51   4.436%   $117.5009   $117.50   $117.50   $117.50  
  7 purchase totals = $851.44       $928.2730   $928.28   $928.20   $928.40