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 $86.42   11.255%   $96.1466   $96.15   $96.15   $96.10  
  Purchase #2 $233.50   4.132%   $243.1482   $243.15   $243.15   $243.10  
  Purchase #3 $232.92   3.709%   $241.559   $241.56   $241.55   $241.60  
  Purchase #4 $98.25   5.184%   $103.3433   $103.34   $103.35   $103.30  
  Purchase #5 $5.94   12.845%   $6.703   $6.70   $6.70   $6.70  
  Purchase #6 $115.79   5.348%   $121.9824   $121.98   $122.00   $122.00  
  Purchase #7 $22.94   10.392%   $25.3239   $25.32   $25.30   $25.30  
  7 purchase totals = $795.76       $838.2064   $838.20   $838.20   $838.10