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 $55.29   11.839%   $61.8358   $61.84   $61.85   $61.80  
  Purchase #2 $64.67   3.589%   $66.991   $66.99   $67.00   $67.00  
  Purchase #3 $178.55   8.107%   $193.025   $193.03   $193.05   $193.00  
  Purchase #4 $238.90   8.677%   $259.6294   $259.63   $259.65   $259.60  
  Purchase #5 $148.32   11.749%   $165.7461   $165.75   $165.75   $165.70  
  Purchase #6 $164.41   11.415%   $183.1774   $183.18   $183.20   $183.20  
  Purchase #7 $20.38   3.818%   $21.1581   $21.16   $21.15   $21.20  
  7 purchase totals = $870.52       $951.5628   $951.58   $951.65   $951.50