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 $109.93   7.393%   $118.0571   $118.06   $118.05   $118.10  
  Purchase #2 $241.82   9.605%   $265.0468   $265.05   $265.05   $265.00  
  Purchase #3 $22.74   12.634%   $25.613   $25.61   $25.60   $25.60  
  Purchase #4 $195.58   6.208%   $207.7216   $207.72   $207.70   $207.70  
  Purchase #5 $109.49   10.654%   $121.1551   $121.16   $121.15   $121.20  
  Purchase #6 $211.70   10.564%   $234.064   $234.06   $234.05   $234.10  
  Purchase #7 $169.70   4.647%   $177.586   $177.59   $177.60   $177.60  
  7 purchase totals = $1,060.96       $1,149.2436   $1,149.25   $1,149.20   $1,149.30