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 $68.84   3.796%   $71.4532   $71.45   $71.45   $71.50  
  Purchase #2 $216.43   8.781%   $235.4347   $235.43   $235.45   $235.40  
  Purchase #3 $11.91   7.732%   $12.8309   $12.83   $12.85   $12.80  
  Purchase #4 $164.39   3.803%   $170.6418   $170.64   $170.65   $170.60  
  Purchase #5 $171.36   11.601%   $191.2395   $191.24   $191.25   $191.20  
  Purchase #6 $193.84   8.280%   $209.89   $209.89   $209.90   $209.90  
  Purchase #7 $120.26   12.111%   $134.8247   $134.82   $134.80   $134.80  
  7 purchase totals = $947.03       $1,026.3148   $1,026.30   $1,026.35   $1,026.20