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 $241.33   7.747%   $260.0258   $260.03   $260.05   $260.00  
  Purchase #2 $164.82   7.521%   $177.2161   $177.22   $177.20   $177.20  
  Purchase #3 $215.43   3.532%   $223.039   $223.04   $223.05   $223.00  
  Purchase #4 $52.34   8.645%   $56.8648   $56.86   $56.85   $56.90  
  Purchase #5 $5.97   3.524%   $6.1804   $6.18   $6.20   $6.20  
  Purchase #6 $191.35   4.769%   $200.4755   $200.48   $200.50   $200.50  
  Purchase #7 $174.80   11.346%   $194.6328   $194.63   $194.65   $194.60  
  7 purchase totals = $1,046.04       $1,118.4344   $1,118.44   $1,118.50   $1,118.40