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 $227.51   10.694%   $251.8399   $251.84   $251.85   $251.80  
  Purchase #2 $193.64   10.411%   $213.7999   $213.80   $213.80   $213.80  
  Purchase #3 $18.33   11.666%   $20.4684   $20.47   $20.45   $20.50  
  Purchase #4 $22.92   6.622%   $24.4378   $24.44   $24.45   $24.40  
  Purchase #5 $23.34   11.294%   $25.976   $25.98   $26.00   $26.00  
  Purchase #6 $145.42   8.665%   $158.0206   $158.02   $158.00   $158.00  
  Purchase #7 $219.81   12.240%   $246.7147   $246.71   $246.70   $246.70  
  7 purchase totals = $850.97       $941.2573   $941.26   $941.25   $941.20