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 $250.88   7.114%   $268.7276   $268.73   $268.75   $268.70  
  Purchase #2 $157.89   8.655%   $171.5554   $171.56   $171.55   $171.60  
  Purchase #3 $113.43   12.424%   $127.5225   $127.52   $127.50   $127.50  
  Purchase #4 $193.67   11.629%   $216.1919   $216.19   $216.20   $216.20  
  Purchase #5 $24.75   7.384%   $26.5775   $26.58   $26.60   $26.60  
  Purchase #6 $190.56   4.350%   $198.8494   $198.85   $198.85   $198.80  
  Purchase #7 $100.86   3.162%   $104.0492   $104.05   $104.05   $104.00  
  7 purchase totals = $1,032.04       $1,113.4735   $1,113.48   $1,113.50   $1,113.40