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 $53.81   13.759%   $61.2137   $61.21   $61.20   $61.20  
  Purchase #2 $182.25   11.743%   $203.6516   $203.65   $203.65   $203.70  
  Purchase #3 $50.56   13.507%   $57.3891   $57.39   $57.40   $57.40  
  Purchase #4 $169.35   9.382%   $185.2384   $185.24   $185.25   $185.20  
  Purchase #5 $128.99   3.325%   $133.2789   $133.28   $133.30   $133.30  
  Purchase #6 $27.45   8.339%   $29.7391   $29.74   $29.75   $29.70  
  Purchase #7 $8.82   5.487%   $9.304   $9.30   $9.30   $9.30  
  7 purchase totals = $621.23       $679.8148   $679.81   $679.85   $679.80