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 $13.69   7.843%   $14.7637   $14.76   $14.75   $14.80  
  Purchase #2 $207.52   12.397%   $233.2463   $233.25   $233.25   $233.20  
  Purchase #3 $56.90   12.525%   $64.0267   $64.03   $64.05   $64.00  
  Purchase #4 $148.79   10.207%   $163.977   $163.98   $164.00   $164.00  
  Purchase #5 $191.37   7.390%   $205.5122   $205.51   $205.50   $205.50  
  Purchase #6 $196.32   12.166%   $220.2043   $220.20   $220.20   $220.20  
  Purchase #7 $15.97   3.744%   $16.5679   $16.57   $16.55   $16.60  
  7 purchase totals = $830.56       $918.2981   $918.30   $918.30   $918.30