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 $76.62   11.600%   $85.5079   $85.51   $85.50   $85.50  
  Purchase #2 $134.89   10.482%   $149.0292   $149.03   $149.05   $149.00  
  Purchase #3 $151.76   7.740%   $163.5062   $163.51   $163.50   $163.50  
  Purchase #4 $131.84   3.269%   $136.1498   $136.15   $136.15   $136.10  
  Purchase #5 $109.77   9.372%   $120.0576   $120.06   $120.05   $120.10  
  Purchase #6 $147.59   9.300%   $161.3159   $161.32   $161.30   $161.30  
  Purchase #7 $131.54   7.549%   $141.47   $141.47   $141.45   $141.50  
  7 purchase totals = $884.01       $957.0366   $957.05   $957.00   $957.00