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 $63.67   12.212%   $71.4454   $71.45   $71.45   $71.40  
  Purchase #2 $216.28   5.386%   $227.9288   $227.93   $227.95   $227.90  
  Purchase #3 $225.92   7.639%   $243.178   $243.18   $243.20   $243.20  
  Purchase #4 $31.74   7.637%   $34.164   $34.16   $34.15   $34.20  
  Purchase #5 $216.76   6.189%   $230.1753   $230.18   $230.20   $230.20  
  Purchase #6 $53.94   5.421%   $56.8641   $56.86   $56.85   $56.90  
  Purchase #7 $215.91   10.452%   $238.4769   $238.48   $238.50   $238.50  
  7 purchase totals = $1,024.22       $1,102.2325   $1,102.24   $1,102.30   $1,102.30