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 $126.98   5.620%   $134.1163   $134.12   $134.10   $134.10  
  Purchase #2 $36.60   7.102%   $39.1993   $39.20   $39.20   $39.20  
  Purchase #3 $111.53   4.610%   $116.6715   $116.67   $116.65   $116.70  
  Purchase #4 $243.47   11.579%   $271.6614   $271.66   $271.65   $271.70  
  Purchase #5 $166.66   4.602%   $174.3297   $174.33   $174.35   $174.30  
  Purchase #6 $143.98   8.445%   $156.1391   $156.14   $156.15   $156.10  
  Purchase #7 $120.83   12.197%   $135.5676   $135.57   $135.55   $135.60  
  7 purchase totals = $950.05       $1,027.6849   $1,027.69   $1,027.65   $1,027.70