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 $61.85   5.658%   $65.3495   $65.35   $65.35   $65.30  
  Purchase #2 $148.35   11.504%   $165.4162   $165.42   $165.40   $165.40  
  Purchase #3 $241.81   3.331%   $249.8647   $249.86   $249.85   $249.90  
  Purchase #4 $229.67   13.869%   $261.5229   $261.52   $261.50   $261.50  
  Purchase #5 $78.41   7.228%   $84.0775   $84.08   $84.10   $84.10  
  Purchase #6 $71.59   11.104%   $79.5394   $79.54   $79.55   $79.50  
  Purchase #7 $96.44   12.327%   $108.3282   $108.33   $108.35   $108.30  
  7 purchase totals = $928.12       $1,014.0984   $1,014.10   $1,014.10   $1,014.00