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 $128.80   6.521%   $137.199   $137.20   $137.20   $137.20  
  Purchase #2 $247.95   10.734%   $274.565   $274.57   $274.55   $274.60  
  Purchase #3 $136.83   4.559%   $143.0681   $143.07   $143.05   $143.10  
  Purchase #4 $88.33   6.123%   $93.7384   $93.74   $93.75   $93.70  
  Purchase #5 $225.55   5.171%   $237.2132   $237.21   $237.20   $237.20  
  Purchase #6 $152.49   5.581%   $161.0005   $161.00   $161.00   $161.00  
  Purchase #7 $211.82   5.747%   $223.9933   $223.99   $224.00   $224.00  
  7 purchase totals = $1,191.77       $1,270.7775   $1,270.78   $1,270.75   $1,270.80