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 $160.37   8.546%   $174.0752   $174.08   $174.10   $174.10  
  Purchase #2 $211.85   13.496%   $240.4413   $240.44   $240.45   $240.40  
  Purchase #3 $115.94   8.723%   $126.0534   $126.05   $126.05   $126.10  
  Purchase #4 $215.40   6.397%   $229.1791   $229.18   $229.20   $229.20  
  Purchase #5 $18.42   7.113%   $19.7302   $19.73   $19.75   $19.70  
  Purchase #6 $230.98   6.692%   $246.4372   $246.44   $246.45   $246.40  
  Purchase #7 $168.65   5.267%   $177.5328   $177.53   $177.55   $177.50  
  7 purchase totals = $1,121.61       $1,213.4492   $1,213.45   $1,213.55   $1,213.40