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 $74.73   10.670%   $82.7037   $82.70   $82.70   $82.70  
  Purchase #2 $243.38   8.496%   $264.0576   $264.06   $264.05   $264.10  
  Purchase #3 $54.56   4.835%   $57.198   $57.20   $57.20   $57.20  
  Purchase #4 $116.29   4.143%   $121.1079   $121.11   $121.10   $121.10  
  Purchase #5 $204.65   6.774%   $218.513   $218.51   $218.50   $218.50  
  Purchase #6 $200.56   6.170%   $212.9346   $212.93   $212.95   $212.90  
  Purchase #7 $117.36   11.394%   $130.732   $130.73   $130.75   $130.70  
  7 purchase totals = $1,011.53       $1,087.2468   $1,087.24   $1,087.25   $1,087.20