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 $187.95   9.428%   $205.6699   $205.67   $205.65   $205.70  
  Purchase #2 $233.33   6.565%   $248.6481   $248.65   $248.65   $248.60  
  Purchase #3 $19.40   10.514%   $21.4397   $21.44   $21.45   $21.40  
  Purchase #4 $58.67   9.336%   $64.1474   $64.15   $64.15   $64.10  
  Purchase #5 $162.75   13.515%   $184.7457   $184.75   $184.75   $184.70  
  Purchase #6 $102.31   12.425%   $115.022   $115.02   $115.00   $115.00  
  Purchase #7 $228.71   7.617%   $246.1308   $246.13   $246.15   $246.10  
  7 purchase totals = $993.12       $1,085.8036   $1,085.81   $1,085.80   $1,085.60