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 $24.45   8.776%   $26.5957   $26.60   $26.60   $26.60  
  Purchase #2 $227.49   11.268%   $253.1236   $253.12   $253.10   $253.10  
  Purchase #3 $187.63   8.619%   $203.8018   $203.80   $203.80   $203.80  
  Purchase #4 $230.78   11.344%   $256.9597   $256.96   $256.95   $257.00  
  Purchase #5 $174.33   3.870%   $181.0766   $181.08   $181.10   $181.10  
  Purchase #6 $216.81   12.205%   $243.2717   $243.27   $243.25   $243.30  
  Purchase #7 $86.89   5.868%   $91.9887   $91.99   $92.00   $92.00  
  7 purchase totals = $1,148.38       $1,256.8178   $1,256.82   $1,256.80   $1,256.90