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 $183.29   11.714%   $204.7606   $204.76   $204.75   $204.80  
  Purchase #2 $172.26   13.847%   $196.1128   $196.11   $196.10   $196.10  
  Purchase #3 $15.64   10.352%   $17.2591   $17.26   $17.25   $17.30  
  Purchase #4 $199.40   8.375%   $216.0998   $216.10   $216.10   $216.10  
  Purchase #5 $44.33   9.600%   $48.5857   $48.59   $48.60   $48.60  
  Purchase #6 $73.96   5.762%   $78.2216   $78.22   $78.20   $78.20  
  Purchase #7 $232.95   3.327%   $240.7002   $240.70   $240.70   $240.70  
  7 purchase totals = $921.83       $1,001.7398   $1,001.74   $1,001.70   $1,001.80