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 $43.51   9.274%   $47.5451   $47.55   $47.55   $47.50  
  Purchase #2 $218.75   13.774%   $248.8806   $248.88   $248.90   $248.90  
  Purchase #3 $86.86   8.618%   $94.3456   $94.35   $94.35   $94.30  
  Purchase #4 $162.61   11.828%   $181.8435   $181.84   $181.85   $181.80  
  Purchase #5 $62.81   8.748%   $68.3046   $68.30   $68.30   $68.30  
  Purchase #6 $122.36   8.303%   $132.5196   $132.52   $132.50   $132.50  
  Purchase #7 $219.55   7.585%   $236.2029   $236.20   $236.20   $236.20  
  7 purchase totals = $916.45       $1,009.6419   $1,009.64   $1,009.65   $1,009.50