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 $106.81   11.632%   $119.2341   $119.23   $119.25   $119.20  
  Purchase #2 $205.38   7.160%   $220.0852   $220.09   $220.10   $220.10  
  Purchase #3 $26.60   5.713%   $28.1197   $28.12   $28.10   $28.10  
  Purchase #4 $211.54   5.870%   $223.9574   $223.96   $223.95   $224.00  
  Purchase #5 $232.58   3.357%   $240.3877   $240.39   $240.40   $240.40  
  Purchase #6 $49.25   13.157%   $55.7298   $55.73   $55.75   $55.70  
  Purchase #7 $114.43   4.692%   $119.7991   $119.80   $119.80   $119.80  
  7 purchase totals = $946.59       $1,007.3130   $1,007.32   $1,007.35   $1,007.30