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 $176.98   8.467%   $191.9649   $191.96   $191.95   $192.00  
  Purchase #2 $52.35   9.381%   $57.261   $57.26   $57.25   $57.30  
  Purchase #3 $121.85   8.234%   $131.8831   $131.88   $131.90   $131.90  
  Purchase #4 $113.72   3.333%   $117.5103   $117.51   $117.50   $117.50  
  Purchase #5 $72.91   8.731%   $79.2758   $79.28   $79.30   $79.30  
  Purchase #6 $56.65   3.510%   $58.6384   $58.64   $58.65   $58.60  
  Purchase #7 $123.77   8.355%   $134.111   $134.11   $134.10   $134.10  
  7 purchase totals = $718.23       $770.6445   $770.64   $770.65   $770.70