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 $231.85   6.759%   $247.5207   $247.52   $247.50   $247.50  
  Purchase #2 $236.38   9.483%   $258.7959   $258.80   $258.80   $258.80  
  Purchase #3 $81.58   3.688%   $84.5887   $84.59   $84.60   $84.60  
  Purchase #4 $27.87   7.466%   $29.9508   $29.95   $29.95   $30.00  
  Purchase #5 $206.64   5.690%   $218.3978   $218.40   $218.40   $218.40  
  Purchase #6 $247.88   8.386%   $268.6672   $268.67   $268.65   $268.70  
  Purchase #7 $94.82   13.296%   $107.4273   $107.43   $107.45   $107.40  
  7 purchase totals = $1,127.02       $1,215.3484   $1,215.36   $1,215.35   $1,215.40