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 $190.26   6.669%   $202.9484   $202.95   $202.95   $202.90  
  Purchase #2 $161.49   13.651%   $183.535   $183.54   $183.55   $183.50  
  Purchase #3 $60.76   8.462%   $65.9015   $65.90   $65.90   $65.90  
  Purchase #4 $56.25   7.518%   $60.4789   $60.48   $60.50   $60.50  
  Purchase #5 $12.74   13.326%   $14.4377   $14.44   $14.45   $14.40  
  Purchase #6 $223.60   4.494%   $233.6486   $233.65   $233.65   $233.60  
  Purchase #7 $235.96   6.439%   $251.1535   $251.15   $251.15   $251.20  
  7 purchase totals = $941.06       $1,012.1036   $1,012.11   $1,012.15   $1,012.00