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 $67.69   11.535%   $75.498   $75.50   $75.50   $75.50  
  Purchase #2 $22.91   3.174%   $23.6372   $23.64   $23.65   $23.60  
  Purchase #3 $71.30   4.704%   $74.654   $74.65   $74.65   $74.70  
  Purchase #4 $205.47   13.180%   $232.5509   $232.55   $232.55   $232.60  
  Purchase #5 $169.36   8.831%   $184.3162   $184.32   $184.30   $184.30  
  Purchase #6 $12.94   4.247%   $13.4896   $13.49   $13.50   $13.50  
  Purchase #7 $202.96   13.585%   $230.5321   $230.53   $230.55   $230.50  
  7 purchase totals = $752.63       $834.6780   $834.68   $834.70   $834.70