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 $98.52   8.349%   $106.7454   $106.75   $106.75   $106.70  
  Purchase #2 $194.41   9.215%   $212.3249   $212.32   $212.30   $212.30  
  Purchase #3 $154.63   5.317%   $162.8517   $162.85   $162.85   $162.90  
  Purchase #4 $33.56   10.307%   $37.019   $37.02   $37.00   $37.00  
  Purchase #5 $111.78   4.397%   $116.695   $116.70   $116.70   $116.70  
  Purchase #6 $83.93   3.291%   $86.6921   $86.69   $86.70   $86.70  
  Purchase #7 $29.72   6.130%   $31.5418   $31.54   $31.55   $31.50  
  7 purchase totals = $706.55       $753.8699   $753.87   $753.85   $753.80