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 $44.30   6.147%   $47.0231   $47.02   $47.00   $47.00  
  Purchase #2 $145.57   13.826%   $165.6965   $165.70   $165.70   $165.70  
  Purchase #3 $156.60   13.814%   $178.2327   $178.23   $178.25   $178.20  
  Purchase #4 $189.62   8.661%   $206.043   $206.04   $206.05   $206.00  
  Purchase #5 $131.96   6.813%   $140.9504   $140.95   $140.95   $141.00  
  Purchase #6 $118.49   8.652%   $128.7418   $128.74   $128.75   $128.70  
  Purchase #7 $55.59   13.787%   $63.2542   $63.25   $63.25   $63.30  
  7 purchase totals = $842.13       $929.9417   $929.93   $929.95   $929.90