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 $55.74   12.793%   $62.8708   $62.87   $62.85   $62.90  
  Purchase #2 $147.63   12.482%   $166.0572   $166.06   $166.05   $166.10  
  Purchase #3 $242.52   11.399%   $270.1649   $270.16   $270.15   $270.20  
  Purchase #4 $31.83   8.411%   $34.5072   $34.51   $34.50   $34.50  
  Purchase #5 $86.45   9.309%   $94.4976   $94.50   $94.50   $94.50  
  Purchase #6 $164.92   11.159%   $183.3234   $183.32   $183.30   $183.30  
  Purchase #7 $218.69   4.707%   $228.9837   $228.98   $229.00   $229.00  
  7 purchase totals = $947.78       $1,040.4048   $1,040.40   $1,040.35   $1,040.50