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 $207.35   12.471%   $233.2086   $233.21   $233.20   $233.20  
  Purchase #2 $123.66   9.452%   $135.3483   $135.35   $135.35   $135.30  
  Purchase #3 $220.37   12.863%   $248.7162   $248.72   $248.70   $248.70  
  Purchase #4 $70.53   11.385%   $78.5598   $78.56   $78.55   $78.60  
  Purchase #5 $25.35   6.297%   $26.9463   $26.95   $26.95   $26.90  
  Purchase #6 $217.65   7.326%   $233.595   $233.60   $233.60   $233.60  
  Purchase #7 $220.47   6.198%   $234.1347   $234.13   $234.15   $234.10  
  7 purchase totals = $1,085.38       $1,190.5089   $1,190.52   $1,190.50   $1,190.40