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 $66.97   4.762%   $70.1591   $70.16   $70.15   $70.20  
  Purchase #2 $160.96   11.256%   $179.0777   $179.08   $179.10   $179.10  
  Purchase #3 $74.98   8.449%   $81.3151   $81.32   $81.30   $81.30  
  Purchase #4 $126.27   12.839%   $142.4818   $142.48   $142.50   $142.50  
  Purchase #5 $40.67   12.323%   $45.6818   $45.68   $45.70   $45.70  
  Purchase #6 $200.29   13.760%   $227.8499   $227.85   $227.85   $227.80  
  Purchase #7 $114.66   10.341%   $126.517   $126.52   $126.50   $126.50  
  7 purchase totals = $784.80       $873.0824   $873.09   $873.10   $873.10