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 $92.32   7.294%   $99.0538   $99.05   $99.05   $99.10  
  Purchase #2 $174.86   4.273%   $182.3318   $182.33   $182.35   $182.30  
  Purchase #3 $56.32   13.157%   $63.73   $63.73   $63.75   $63.70  
  Purchase #4 $222.46   9.353%   $243.2667   $243.27   $243.25   $243.30  
  Purchase #5 $169.88   12.493%   $191.1031   $191.10   $191.10   $191.10  
  Purchase #6 $242.36   11.713%   $270.7476   $270.75   $270.75   $270.70  
  Purchase #7 $175.64   10.629%   $194.3088   $194.31   $194.30   $194.30  
  7 purchase totals = $1,133.84       $1,244.5418   $1,244.54   $1,244.55   $1,244.50