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 $34.88   7.487%   $37.4915   $37.49   $37.50   $37.50  
  Purchase #2 $109.77   6.472%   $116.8743   $116.87   $116.85   $116.90  
  Purchase #3 $63.58   7.435%   $68.3072   $68.31   $68.30   $68.30  
  Purchase #4 $101.98   8.106%   $110.2465   $110.25   $110.25   $110.20  
  Purchase #5 $112.30   10.493%   $124.0836   $124.08   $124.10   $124.10  
  Purchase #6 $238.51   11.684%   $266.3775   $266.38   $266.40   $266.40  
  Purchase #7 $218.82   11.103%   $243.1156   $243.12   $243.10   $243.10  
  7 purchase totals = $879.84       $966.4962   $966.50   $966.50   $966.50