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 $153.92   13.828%   $175.2041   $175.20   $175.20   $175.20  
  Purchase #2 $164.82   4.676%   $172.527   $172.53   $172.55   $172.50  
  Purchase #3 $14.35   3.867%   $14.9049   $14.90   $14.90   $14.90  
  Purchase #4 $173.27   4.305%   $180.7293   $180.73   $180.75   $180.70  
  Purchase #5 $55.58   12.369%   $62.4547   $62.45   $62.45   $62.50  
  Purchase #6 $241.64   9.247%   $263.9845   $263.98   $264.00   $264.00  
  Purchase #7 $176.42   8.350%   $191.1511   $191.15   $191.15   $191.20  
  7 purchase totals = $980.00       $1,060.9556   $1,060.94   $1,061.00   $1,061.00