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 $69.95   12.301%   $78.5545   $78.55   $78.55   $78.60  
  Purchase #2 $153.88   10.259%   $169.6665   $169.67   $169.65   $169.70  
  Purchase #3 $127.53   8.755%   $138.6953   $138.70   $138.70   $138.70  
  Purchase #4 $147.32   12.874%   $166.286   $166.29   $166.30   $166.30  
  Purchase #5 $154.47   10.156%   $170.158   $170.16   $170.15   $170.20  
  Purchase #6 $201.43   6.388%   $214.2973   $214.30   $214.30   $214.30  
  Purchase #7 $84.97   13.478%   $96.4223   $96.42   $96.40   $96.40  
  7 purchase totals = $939.55       $1,034.0799   $1,034.09   $1,034.05   $1,034.20