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 $81.83   4.216%   $85.28   $85.28   $85.30   $85.30  
  Purchase #2 $101.85   5.684%   $107.6392   $107.64   $107.65   $107.60  
  Purchase #3 $23.35   5.435%   $24.6191   $24.62   $24.60   $24.60  
  Purchase #4 $201.61   8.376%   $218.4969   $218.50   $218.50   $218.50  
  Purchase #5 $116.39   13.457%   $132.0526   $132.05   $132.05   $132.10  
  Purchase #6 $206.41   13.658%   $234.6015   $234.60   $234.60   $234.60  
  Purchase #7 $147.61   12.343%   $165.8295   $165.83   $165.85   $165.80  
  7 purchase totals = $879.05       $968.5188   $968.52   $968.55   $968.50