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 $108.73   10.338%   $119.9705   $119.97   $119.95   $120.00  
  Purchase #2 $196.42   7.376%   $210.9079   $210.91   $210.90   $210.90  
  Purchase #3 $247.88   11.416%   $276.178   $276.18   $276.20   $276.20  
  Purchase #4 $99.25   8.676%   $107.8609   $107.86   $107.85   $107.90  
  Purchase #5 $76.96   3.867%   $79.936   $79.94   $79.95   $79.90  
  Purchase #6 $78.81   13.529%   $89.4722   $89.47   $89.45   $89.50  
  Purchase #7 $221.39   10.571%   $244.7931   $244.79   $244.80   $244.80  
  7 purchase totals = $1,029.44       $1,129.1186   $1,129.12   $1,129.10   $1,129.20