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 $246.77   6.861%   $263.7009   $263.70   $263.70   $263.70  
  Purchase #2 $165.86   7.543%   $178.3708   $178.37   $178.35   $178.40  
  Purchase #3 $129.86   6.484%   $138.2801   $138.28   $138.30   $138.30  
  Purchase #4 $228.42   7.812%   $246.2642   $246.26   $246.25   $246.30  
  Purchase #5 $81.79   9.365%   $89.4496   $89.45   $89.45   $89.40  
  Purchase #6 $94.62   10.413%   $104.4728   $104.47   $104.45   $104.50  
  Purchase #7 $154.95   8.292%   $167.7985   $167.80   $167.80   $167.80  
  7 purchase totals = $1,102.27       $1,188.3369   $1,188.33   $1,188.30   $1,188.40