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 $86.33   7.351%   $92.6761   $92.68   $92.70   $92.70  
  Purchase #2 $142.60   6.114%   $151.3186   $151.32   $151.30   $151.30  
  Purchase #3 $178.62   6.586%   $190.3839   $190.38   $190.40   $190.40  
  Purchase #4 $209.77   12.595%   $236.1905   $236.19   $236.20   $236.20  
  Purchase #5 $71.64   12.287%   $80.4424   $80.44   $80.45   $80.40  
  Purchase #6 $132.51   10.104%   $145.8988   $145.90   $145.90   $145.90  
  Purchase #7 $31.89   5.621%   $33.6825   $33.68   $33.70   $33.70  
  7 purchase totals = $853.36       $930.5928   $930.59   $930.65   $930.60