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 $61.57   9.119%   $67.1846   $67.18   $67.20   $67.20  
  Purchase #2 $230.29   12.705%   $259.5483   $259.55   $259.55   $259.50  
  Purchase #3 $110.35   5.566%   $116.4921   $116.49   $116.50   $116.50  
  Purchase #4 $24.85   6.516%   $26.4692   $26.47   $26.45   $26.50  
  Purchase #5 $117.85   3.120%   $121.5269   $121.53   $121.55   $121.50  
  Purchase #6 $13.98   6.269%   $14.8564   $14.86   $14.85   $14.90  
  Purchase #7 $228.63   8.214%   $247.4097   $247.41   $247.40   $247.40  
  7 purchase totals = $787.52       $853.4872   $853.49   $853.50   $853.50