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 $153.48   11.383%   $170.9506   $170.95   $170.95   $171.00  
  Purchase #2 $214.74   13.421%   $243.5603   $243.56   $243.55   $243.60  
  Purchase #3 $147.92   13.738%   $168.2412   $168.24   $168.25   $168.20  
  Purchase #4 $231.64   7.323%   $248.603   $248.60   $248.60   $248.60  
  Purchase #5 $133.31   13.810%   $151.7201   $151.72   $151.70   $151.70  
  Purchase #6 $42.59   10.613%   $47.1101   $47.11   $47.10   $47.10  
  Purchase #7 $74.44   13.291%   $84.3338   $84.33   $84.35   $84.30  
  7 purchase totals = $998.12       $1,114.5191   $1,114.51   $1,114.50   $1,114.50