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 $243.84   4.811%   $255.5711   $255.57   $255.55   $255.60  
  Purchase #2 $98.36   7.768%   $106.0006   $106.00   $106.00   $106.00  
  Purchase #3 $80.99   13.441%   $91.8759   $91.88   $91.90   $91.90  
  Purchase #4 $198.88   12.789%   $224.3148   $224.31   $224.30   $224.30  
  Purchase #5 $193.60   13.443%   $219.6256   $219.63   $219.65   $219.60  
  Purchase #6 $240.85   8.349%   $260.9586   $260.96   $260.95   $261.00  
  Purchase #7 $90.51   4.740%   $94.8002   $94.80   $94.80   $94.80  
  7 purchase totals = $1,147.03       $1,253.1468   $1,253.15   $1,253.15   $1,253.20