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 $184.62   13.360%   $209.2852   $209.29   $209.30   $209.30  
  Purchase #2 $148.98   9.631%   $163.3283   $163.33   $163.35   $163.30  
  Purchase #3 $148.85   3.343%   $153.8261   $153.83   $153.85   $153.80  
  Purchase #4 $72.62   9.848%   $79.7716   $79.77   $79.75   $79.80  
  Purchase #5 $9.81   13.680%   $11.152   $11.15   $11.15   $11.20  
  Purchase #6 $145.81   3.432%   $150.8142   $150.81   $150.80   $150.80  
  Purchase #7 $217.96   11.630%   $243.3087   $243.31   $243.30   $243.30  
  7 purchase totals = $928.65       $1,011.4861   $1,011.49   $1,011.50   $1,011.50