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 $218.48   6.716%   $233.1531   $233.15   $233.15   $233.20  
  Purchase #2 $192.84   4.820%   $202.1349   $202.13   $202.15   $202.10  
  Purchase #3 $52.52   9.623%   $57.574   $57.57   $57.55   $57.60  
  Purchase #4 $95.58   12.800%   $107.8142   $107.81   $107.80   $107.80  
  Purchase #5 $8.97   4.234%   $9.3498   $9.35   $9.35   $9.30  
  Purchase #6 $133.95   5.233%   $140.9596   $140.96   $140.95   $141.00  
  Purchase #7 $245.77   12.518%   $276.5355   $276.54   $276.55   $276.50  
  7 purchase totals = $948.11       $1,027.5211   $1,027.51   $1,027.50   $1,027.50