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 $200.98   6.431%   $213.905   $213.91   $213.90   $213.90  
  Purchase #2 $108.77   9.220%   $118.7986   $118.80   $118.80   $118.80  
  Purchase #3 $214.99   5.427%   $226.6575   $226.66   $226.65   $226.70  
  Purchase #4 $156.94   4.146%   $163.4467   $163.45   $163.45   $163.40  
  Purchase #5 $163.60   12.731%   $184.4279   $184.43   $184.45   $184.40  
  Purchase #6 $175.63   13.418%   $199.196   $199.20   $199.20   $199.20  
  Purchase #7 $233.91   11.144%   $259.9769   $259.98   $260.00   $260.00  
  7 purchase totals = $1,254.82       $1,366.4086   $1,366.43   $1,366.45   $1,366.40