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 $153.67   4.309%   $160.2916   $160.29   $160.30   $160.30  
  Purchase #2 $29.40   6.715%   $31.3742   $31.37   $31.35   $31.40  
  Purchase #3 $107.52   7.815%   $115.9227   $115.92   $115.90   $115.90  
  Purchase #4 $141.44   11.825%   $158.1653   $158.17   $158.15   $158.20  
  Purchase #5 $148.79   6.674%   $158.7202   $158.72   $158.70   $158.70  
  Purchase #6 $9.96   6.712%   $10.6285   $10.63   $10.65   $10.60  
  Purchase #7 $182.25   11.564%   $203.3254   $203.33   $203.35   $203.30  
  7 purchase totals = $773.03       $838.4279   $838.43   $838.40   $838.40