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 $151.77   10.416%   $167.5784   $167.58   $167.60   $167.60  
  Purchase #2 $102.98   13.464%   $116.8452   $116.85   $116.85   $116.80  
  Purchase #3 $169.81   6.813%   $181.3792   $181.38   $181.40   $181.40  
  Purchase #4 $129.59   12.400%   $145.6592   $145.66   $145.65   $145.70  
  Purchase #5 $169.89   11.604%   $189.604   $189.60   $189.60   $189.60  
  Purchase #6 $34.97   8.510%   $37.9459   $37.95   $37.95   $37.90  
  Purchase #7 $60.74   5.313%   $63.9671   $63.97   $63.95   $64.00  
  7 purchase totals = $819.75       $902.9790   $902.99   $903.00   $903.00