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 $160.67   13.467%   $182.3074   $182.31   $182.30   $182.30  
  Purchase #2 $174.76   11.354%   $194.6023   $194.60   $194.60   $194.60  
  Purchase #3 $242.94   11.401%   $270.6376   $270.64   $270.65   $270.60  
  Purchase #4 $109.77   13.576%   $124.6724   $124.67   $124.65   $124.70  
  Purchase #5 $205.93   9.808%   $226.1276   $226.13   $226.15   $226.10  
  Purchase #6 $102.47   9.725%   $112.4352   $112.44   $112.45   $112.40  
  Purchase #7 $70.43   7.390%   $75.6348   $75.63   $75.65   $75.60  
  7 purchase totals = $1,066.97       $1,186.4173   $1,186.42   $1,186.45   $1,186.30