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 $224.92   3.665%   $233.1633   $233.16   $233.15   $233.20  
  Purchase #2 $183.99   11.591%   $205.3163   $205.32   $205.30   $205.30  
  Purchase #3 $230.83   10.467%   $254.991   $254.99   $255.00   $255.00  
  Purchase #4 $142.38   12.325%   $159.9283   $159.93   $159.95   $159.90  
  Purchase #5 $209.27   9.701%   $229.5713   $229.57   $229.55   $229.60  
  Purchase #6 $56.50   13.350%   $64.0428   $64.04   $64.05   $64.00  
  Purchase #7 $110.99   11.488%   $123.7405   $123.74   $123.75   $123.70  
  7 purchase totals = $1,158.88       $1,270.7535   $1,270.75   $1,270.75   $1,270.70