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 $71.30   3.210%   $73.5887   $73.59   $73.60   $73.60  
  Purchase #2 $247.46   7.165%   $265.1905   $265.19   $265.20   $265.20  
  Purchase #3 $67.29   9.500%   $73.6826   $73.68   $73.70   $73.70  
  Purchase #4 $58.85   7.836%   $63.4615   $63.46   $63.45   $63.50  
  Purchase #5 $66.70   8.650%   $72.4696   $72.47   $72.45   $72.50  
  Purchase #6 $183.95   9.842%   $202.0544   $202.05   $202.05   $202.10  
  Purchase #7 $95.37   8.106%   $103.1007   $103.10   $103.10   $103.10  
  7 purchase totals = $790.92       $853.5480   $853.54   $853.55   $853.70