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 $32.39   5.139%   $34.0545   $34.05   $34.05   $34.10  
  Purchase #2 $120.41   7.446%   $129.3757   $129.38   $129.40   $129.40  
  Purchase #3 $249.89   8.303%   $270.6384   $270.64   $270.65   $270.60  
  Purchase #4 $102.99   13.545%   $116.94   $116.94   $116.95   $116.90  
  Purchase #5 $152.83   13.862%   $174.0153   $174.02   $174.00   $174.00  
  Purchase #6 $56.97   13.194%   $64.4866   $64.49   $64.50   $64.50  
  Purchase #7 $212.27   11.580%   $236.8509   $236.85   $236.85   $236.90  
  7 purchase totals = $927.75       $1,026.3614   $1,026.37   $1,026.40   $1,026.40