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 $219.95   12.389%   $247.1996   $247.20   $247.20   $247.20  
  Purchase #2 $25.32   11.425%   $28.2128   $28.21   $28.20   $28.20  
  Purchase #3 $81.58   12.795%   $92.0182   $92.02   $92.00   $92.00  
  Purchase #4 $245.37   12.582%   $276.2425   $276.24   $276.25   $276.20  
  Purchase #5 $103.33   10.341%   $114.0154   $114.02   $114.00   $114.00  
  Purchase #6 $77.74   12.674%   $87.5928   $87.59   $87.60   $87.60  
  Purchase #7 $46.38   12.166%   $52.0226   $52.02   $52.00   $52.00  
  7 purchase totals = $799.67       $897.3039   $897.30   $897.25   $897.20