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 $208.96   11.409%   $232.8002   $232.80   $232.80   $232.80  
  Purchase #2 $188.90   5.179%   $198.6831   $198.68   $198.70   $198.70  
  Purchase #3 $92.27   12.368%   $103.682   $103.68   $103.70   $103.70  
  Purchase #4 $49.46   10.102%   $54.4564   $54.46   $54.45   $54.50  
  Purchase #5 $58.85   3.143%   $60.6997   $60.70   $60.70   $60.70  
  Purchase #6 $95.31   9.734%   $104.5875   $104.59   $104.60   $104.60  
  Purchase #7 $241.37   12.500%   $271.5413   $271.54   $271.55   $271.50  
  7 purchase totals = $935.12       $1,026.4502   $1,026.45   $1,026.50   $1,026.50