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 $62.82   5.760%   $66.4384   $66.44   $66.45   $66.40  
  Purchase #2 $44.37   10.691%   $49.1136   $49.11   $49.10   $49.10  
  Purchase #3 $245.64   5.632%   $259.4744   $259.47   $259.45   $259.50  
  Purchase #4 $123.61   9.570%   $135.4395   $135.44   $135.45   $135.40  
  Purchase #5 $130.79   9.535%   $143.2608   $143.26   $143.25   $143.30  
  Purchase #6 $181.86   6.401%   $193.5009   $193.50   $193.50   $193.50  
  Purchase #7 $199.69   11.706%   $223.0657   $223.07   $223.05   $223.10  
  7 purchase totals = $988.78       $1,070.2933   $1,070.29   $1,070.25   $1,070.30