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 $164.95   11.744%   $184.3217   $184.32   $184.30   $184.30  
  Purchase #2 $186.39   13.488%   $211.5303   $211.53   $211.55   $211.50  
  Purchase #3 $22.52   4.581%   $23.5516   $23.55   $23.55   $23.60  
  Purchase #4 $25.65   4.240%   $26.7376   $26.74   $26.75   $26.70  
  Purchase #5 $39.52   11.847%   $44.2019   $44.20   $44.20   $44.20  
  Purchase #6 $17.96   4.419%   $18.7537   $18.75   $18.75   $18.80  
  Purchase #7 $69.55   6.637%   $74.166   $74.17   $74.15   $74.20  
  7 purchase totals = $526.54       $583.2628   $583.26   $583.25   $583.30