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 $58.85   6.393%   $62.6123   $62.61   $62.60   $62.60  
  Purchase #2 $138.73   7.258%   $148.799   $148.80   $148.80   $148.80  
  Purchase #3 $13.59   12.836%   $15.3344   $15.33   $15.35   $15.30  
  Purchase #4 $161.78   3.135%   $166.8518   $166.85   $166.85   $166.90  
  Purchase #5 $157.87   6.155%   $167.5869   $167.59   $167.60   $167.60  
  Purchase #6 $193.30   13.713%   $219.8072   $219.81   $219.80   $219.80  
  Purchase #7 $160.56   3.486%   $166.1571   $166.16   $166.15   $166.20  
  7 purchase totals = $884.68       $947.1487   $947.15   $947.15   $947.20