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 $126.59   6.703%   $135.0753   $135.08   $135.10   $135.10  
  Purchase #2 $8.56   9.285%   $9.3548   $9.35   $9.35   $9.40  
  Purchase #3 $74.80   7.623%   $80.502   $80.50   $80.50   $80.50  
  Purchase #4 $62.93   10.849%   $69.7573   $69.76   $69.75   $69.80  
  Purchase #5 $7.25   12.812%   $8.1789   $8.18   $8.20   $8.20  
  Purchase #6 $223.63   8.760%   $243.22   $243.22   $243.20   $243.20  
  Purchase #7 $192.28   9.119%   $209.814   $209.81   $209.80   $209.80  
  7 purchase totals = $696.04       $755.9023   $755.90   $755.90   $756.00