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 $228.87   12.608%   $257.7259   $257.73   $257.75   $257.70  
  Purchase #2 $179.76   11.173%   $199.8446   $199.84   $199.85   $199.80  
  Purchase #3 $76.93   11.763%   $85.9793   $85.98   $86.00   $86.00  
  Purchase #4 $165.44   3.396%   $171.0583   $171.06   $171.05   $171.10  
  Purchase #5 $197.85   10.839%   $219.295   $219.30   $219.30   $219.30  
  Purchase #6 $97.90   3.142%   $100.976   $100.98   $101.00   $101.00  
  Purchase #7 $169.73   12.378%   $190.7392   $190.74   $190.75   $190.70  
  7 purchase totals = $1,116.48       $1,225.6183   $1,225.63   $1,225.70   $1,225.60