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 $43.33   13.118%   $49.014   $49.01   $49.00   $49.00  
  Purchase #2 $148.35   11.397%   $165.2574   $165.26   $165.25   $165.30  
  Purchase #3 $75.91   11.781%   $84.853   $84.85   $84.85   $84.90  
  Purchase #4 $201.60   5.683%   $213.0569   $213.06   $213.05   $213.10  
  Purchase #5 $190.70   9.840%   $209.4649   $209.46   $209.45   $209.50  
  Purchase #6 $174.28   5.534%   $183.9247   $183.92   $183.90   $183.90  
  Purchase #7 $20.46   10.334%   $22.5743   $22.57   $22.55   $22.60  
  7 purchase totals = $854.63       $928.1452   $928.13   $928.05   $928.30