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 $232.37   9.279%   $253.9316   $253.93   $253.95   $253.90  
  Purchase #2 $14.99   7.136%   $16.0597   $16.06   $16.05   $16.10  
  Purchase #3 $228.48   6.529%   $243.3975   $243.40   $243.40   $243.40  
  Purchase #4 $199.75   6.470%   $212.6738   $212.67   $212.65   $212.70  
  Purchase #5 $47.81   10.821%   $52.9835   $52.98   $53.00   $53.00  
  Purchase #6 $226.86   10.691%   $251.1136   $251.11   $251.10   $251.10  
  Purchase #7 $130.73   9.648%   $143.3428   $143.34   $143.35   $143.30  
  7 purchase totals = $1,080.99       $1,173.5025   $1,173.49   $1,173.50   $1,173.50