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 $8.85   8.329%   $9.5871   $9.59   $9.60   $9.60  
  Purchase #2 $231.35   5.123%   $243.2021   $243.20   $243.20   $243.20  
  Purchase #3 $91.70   10.523%   $101.3496   $101.35   $101.35   $101.30  
  Purchase #4 $106.89   3.250%   $110.3639   $110.36   $110.35   $110.40  
  Purchase #5 $132.82   11.750%   $148.4264   $148.43   $148.45   $148.40  
  Purchase #6 $205.80   6.670%   $219.5269   $219.53   $219.55   $219.50  
  Purchase #7 $218.81   4.180%   $227.9563   $227.96   $227.95   $228.00  
  7 purchase totals = $996.22       $1,060.4123   $1,060.42   $1,060.45   $1,060.40