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 $202.51   8.609%   $219.9441   $219.94   $219.95   $219.90  
  Purchase #2 $202.50   6.484%   $215.6301   $215.63   $215.65   $215.60  
  Purchase #3 $23.46   10.383%   $25.8959   $25.90   $25.90   $25.90  
  Purchase #4 $95.92   12.196%   $107.6184   $107.62   $107.60   $107.60  
  Purchase #5 $238.55   10.601%   $263.8387   $263.84   $263.85   $263.80  
  Purchase #6 $91.51   6.736%   $97.6741   $97.67   $97.65   $97.70  
  Purchase #7 $205.58   9.270%   $224.6373   $224.64   $224.65   $224.60  
  7 purchase totals = $1,060.03       $1,155.2386   $1,155.24   $1,155.25   $1,155.10