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 $98.31   11.853%   $109.9627   $109.96   $109.95   $110.00  
  Purchase #2 $237.75   13.265%   $269.2875   $269.29   $269.30   $269.30  
  Purchase #3 $33.72   12.301%   $37.8679   $37.87   $37.85   $37.90  
  Purchase #4 $119.67   4.364%   $124.8924   $124.89   $124.90   $124.90  
  Purchase #5 $131.43   13.619%   $149.3295   $149.33   $149.35   $149.30  
  Purchase #6 $187.34   5.215%   $197.1098   $197.11   $197.10   $197.10  
  Purchase #7 $71.48   12.657%   $80.5272   $80.53   $80.55   $80.50  
  7 purchase totals = $879.70       $968.9770   $968.98   $969.00   $969.00