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 $192.95   6.310%   $205.1251   $205.13   $205.15   $205.10  
  Purchase #2 $244.38   8.249%   $264.5389   $264.54   $264.55   $264.50  
  Purchase #3 $169.95   7.473%   $182.6504   $182.65   $182.65   $182.70  
  Purchase #4 $145.51   5.460%   $153.4548   $153.45   $153.45   $153.50  
  Purchase #5 $179.77   9.146%   $196.2118   $196.21   $196.20   $196.20  
  Purchase #6 $168.48   8.210%   $182.3122   $182.31   $182.30   $182.30  
  Purchase #7 $130.54   8.554%   $141.7064   $141.71   $141.70   $141.70  
  7 purchase totals = $1,231.58       $1,325.9996   $1,326.00   $1,326.00   $1,326.00