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 $54.26   6.147%   $57.5954   $57.60   $57.60   $57.60  
  Purchase #2 $154.99   12.729%   $174.7187   $174.72   $174.70   $174.70  
  Purchase #3 $120.43   4.597%   $125.9662   $125.97   $125.95   $126.00  
  Purchase #4 $192.33   5.189%   $202.31   $202.31   $202.30   $202.30  
  Purchase #5 $112.35   9.749%   $123.303   $123.30   $123.30   $123.30  
  Purchase #6 $234.31   4.425%   $244.6782   $244.68   $244.70   $244.70  
  Purchase #7 $206.34   3.165%   $212.8707   $212.87   $212.85   $212.90  
  7 purchase totals = $1,075.01       $1,141.4422   $1,141.45   $1,141.40   $1,141.50