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 $182.70   12.588%   $205.6983   $205.70   $205.70   $205.70  
  Purchase #2 $92.94   12.837%   $104.8707   $104.87   $104.85   $104.90  
  Purchase #3 $124.67   6.350%   $132.5865   $132.59   $132.60   $132.60  
  Purchase #4 $194.64   5.448%   $205.244   $205.24   $205.25   $205.20  
  Purchase #5 $158.50   11.511%   $176.7449   $176.74   $176.75   $176.70  
  Purchase #6 $223.29   8.657%   $242.6202   $242.62   $242.60   $242.60  
  Purchase #7 $180.31   12.567%   $202.9696   $202.97   $202.95   $203.00  
  7 purchase totals = $1,157.05       $1,270.7342   $1,270.73   $1,270.70   $1,270.70