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 $236.56   11.108%   $262.8371   $262.84   $262.85   $262.80  
  Purchase #2 $202.47   6.331%   $215.2884   $215.29   $215.30   $215.30  
  Purchase #3 $95.76   8.538%   $103.936   $103.94   $103.95   $103.90  
  Purchase #4 $11.45   12.428%   $12.873   $12.87   $12.85   $12.90  
  Purchase #5 $34.29   11.662%   $38.2889   $38.29   $38.30   $38.30  
  Purchase #6 $163.31   8.471%   $177.144   $177.14   $177.15   $177.10  
  Purchase #7 $62.51   13.460%   $70.9238   $70.92   $70.90   $70.90  
  7 purchase totals = $806.35       $881.2912   $881.29   $881.30   $881.20