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 $231.68   8.849%   $252.1814   $252.18   $252.20   $252.20  
  Purchase #2 $110.94   7.187%   $118.9133   $118.91   $118.90   $118.90  
  Purchase #3 $12.93   12.586%   $14.5574   $14.56   $14.55   $14.60  
  Purchase #4 $148.98   12.559%   $167.6904   $167.69   $167.70   $167.70  
  Purchase #5 $188.79   13.374%   $214.0388   $214.04   $214.05   $214.00  
  Purchase #6 $114.74   9.715%   $125.887   $125.89   $125.90   $125.90  
  Purchase #7 $69.37   4.582%   $72.5485   $72.55   $72.55   $72.50  
  7 purchase totals = $877.43       $965.8168   $965.82   $965.85   $965.80