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 $236.86   11.579%   $264.286   $264.29   $264.30   $264.30  
  Purchase #2 $25.52   3.834%   $26.4984   $26.50   $26.50   $26.50  
  Purchase #3 $106.99   13.435%   $121.3641   $121.36   $121.35   $121.40  
  Purchase #4 $42.99   4.325%   $44.8493   $44.85   $44.85   $44.80  
  Purchase #5 $65.62   7.677%   $70.6576   $70.66   $70.65   $70.70  
  Purchase #6 $165.35   8.254%   $178.998   $179.00   $179.00   $179.00  
  Purchase #7 $222.47   11.134%   $247.2398   $247.24   $247.25   $247.20  
  7 purchase totals = $865.80       $953.8932   $953.90   $953.90   $953.90