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 $225.93   10.227%   $249.0359   $249.04   $249.05   $249.00  
  Purchase #2 $99.79   4.261%   $104.0421   $104.04   $104.05   $104.00  
  Purchase #3 $183.48   5.388%   $193.3659   $193.37   $193.35   $193.40  
  Purchase #4 $162.90   3.783%   $169.0625   $169.06   $169.05   $169.10  
  Purchase #5 $163.42   13.819%   $186.003   $186.00   $186.00   $186.00  
  Purchase #6 $79.60   11.103%   $88.438   $88.44   $88.45   $88.40  
  Purchase #7 $25.46   12.440%   $28.6272   $28.63   $28.65   $28.60  
  7 purchase totals = $940.58       $1,018.5746   $1,018.58   $1,018.60   $1,018.50