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 $165.59   9.517%   $181.3492   $181.35   $181.35   $181.30  
  Purchase #2 $83.51   5.319%   $87.9519   $87.95   $87.95   $88.00  
  Purchase #3 $19.69   13.605%   $22.3688   $22.37   $22.35   $22.40  
  Purchase #4 $69.26   5.213%   $72.8705   $72.87   $72.85   $72.90  
  Purchase #5 $164.65   6.389%   $175.1695   $175.17   $175.15   $175.20  
  Purchase #6 $75.84   11.696%   $84.7102   $84.71   $84.70   $84.70  
  Purchase #7 $236.39   5.819%   $250.1455   $250.15   $250.15   $250.10  
  7 purchase totals = $814.93       $874.5656   $874.57   $874.50   $874.60