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 $203.95   10.119%   $224.5877   $224.59   $224.60   $224.60  
  Purchase #2 $67.63   10.435%   $74.6872   $74.69   $74.70   $74.70  
  Purchase #3 $38.39   3.749%   $39.8292   $39.83   $39.85   $39.80  
  Purchase #4 $235.33   8.348%   $254.9753   $254.98   $255.00   $255.00  
  Purchase #5 $162.43   5.426%   $171.2435   $171.24   $171.25   $171.20  
  Purchase #6 $103.63   10.819%   $114.8417   $114.84   $114.85   $114.80  
  Purchase #7 $201.42   7.682%   $216.8931   $216.89   $216.90   $216.90  
  7 purchase totals = $1,012.78       $1,097.0577   $1,097.06   $1,097.15   $1,097.00