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 $151.77   6.111%   $161.0447   $161.04   $161.05   $161.00  
  Purchase #2 $179.94   10.424%   $198.6969   $198.70   $198.70   $198.70  
  Purchase #3 $172.45   3.198%   $177.965   $177.97   $177.95   $178.00  
  Purchase #4 $179.47   8.565%   $194.8416   $194.84   $194.85   $194.80  
  Purchase #5 $46.59   6.192%   $49.4749   $49.47   $49.45   $49.50  
  Purchase #6 $191.88   9.323%   $209.769   $209.77   $209.75   $209.80  
  Purchase #7 $125.91   4.873%   $132.0456   $132.05   $132.05   $132.00  
  7 purchase totals = $1,048.01       $1,123.8377   $1,123.84   $1,123.80   $1,123.80