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 $224.43   13.421%   $254.5508   $254.55   $254.55   $254.60  
  Purchase #2 $79.70   9.398%   $87.1902   $87.19   $87.20   $87.20  
  Purchase #3 $162.32   3.623%   $168.2009   $168.20   $168.20   $168.20  
  Purchase #4 $194.60   11.774%   $217.5122   $217.51   $217.50   $217.50  
  Purchase #5 $161.97   5.566%   $170.9853   $170.99   $171.00   $171.00  
  Purchase #6 $24.48   7.594%   $26.339   $26.34   $26.35   $26.30  
  Purchase #7 $93.70   8.764%   $101.9119   $101.91   $101.90   $101.90  
  7 purchase totals = $941.20       $1,026.6903   $1,026.69   $1,026.70   $1,026.70