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 $196.48   11.384%   $218.8473   $218.85   $218.85   $218.80  
  Purchase #2 $74.34   13.266%   $84.2019   $84.20   $84.20   $84.20  
  Purchase #3 $245.49   7.817%   $264.68   $264.68   $264.70   $264.70  
  Purchase #4 $231.91   9.145%   $253.1182   $253.12   $253.10   $253.10  
  Purchase #5 $93.90   6.603%   $100.1002   $100.10   $100.10   $100.10  
  Purchase #6 $108.38   13.562%   $123.0785   $123.08   $123.10   $123.10  
  Purchase #7 $208.92   7.847%   $225.314   $225.31   $225.30   $225.30  
  7 purchase totals = $1,159.42       $1,269.3401   $1,269.34   $1,269.35   $1,269.30