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 $102.26   5.290%   $107.6696   $107.67   $107.65   $107.70  
  Purchase #2 $176.87   13.621%   $200.9615   $200.96   $200.95   $201.00  
  Purchase #3 $248.55   4.119%   $258.7878   $258.79   $258.80   $258.80  
  Purchase #4 $65.69   11.211%   $73.0545   $73.05   $73.05   $73.10  
  Purchase #5 $226.60   3.242%   $233.9464   $233.95   $233.95   $233.90  
  Purchase #6 $131.40   4.712%   $137.5916   $137.59   $137.60   $137.60  
  Purchase #7 $177.93   13.252%   $201.5093   $201.51   $201.50   $201.50  
  7 purchase totals = $1,129.30       $1,213.5207   $1,213.52   $1,213.50   $1,213.60