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 $85.77   8.775%   $93.2963   $93.30   $93.30   $93.30  
  Purchase #2 $184.91   3.519%   $191.417   $191.42   $191.40   $191.40  
  Purchase #3 $191.46   3.821%   $198.7757   $198.78   $198.80   $198.80  
  Purchase #4 $105.53   5.376%   $111.2033   $111.20   $111.20   $111.20  
  Purchase #5 $98.39   11.475%   $109.6803   $109.68   $109.70   $109.70  
  Purchase #6 $173.78   12.315%   $195.181   $195.18   $195.20   $195.20  
  Purchase #7 $185.43   4.406%   $193.6   $193.60   $193.60   $193.60  
  7 purchase totals = $1,025.27       $1,093.1536   $1,093.16   $1,093.20   $1,093.20