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 $70.64   7.874%   $76.2022   $76.20   $76.20   $76.20  
  Purchase #2 $104.90   13.112%   $118.6545   $118.65   $118.65   $118.70  
  Purchase #3 $63.42   6.694%   $67.6653   $67.67   $67.65   $67.70  
  Purchase #4 $249.57   6.454%   $265.6772   $265.68   $265.70   $265.70  
  Purchase #5 $224.39   12.773%   $253.0513   $253.05   $253.05   $253.10  
  Purchase #6 $216.30   6.360%   $230.0567   $230.06   $230.05   $230.10  
  Purchase #7 $67.31   3.760%   $69.8409   $69.84   $69.85   $69.80  
  7 purchase totals = $996.53       $1,081.1481   $1,081.15   $1,081.15   $1,081.30