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 $148.99   10.499%   $164.6325   $164.63   $164.65   $164.60  
  Purchase #2 $129.82   8.334%   $140.6392   $140.64   $140.65   $140.60  
  Purchase #3 $81.59   3.288%   $84.2727   $84.27   $84.25   $84.30  
  Purchase #4 $178.87   6.185%   $189.9331   $189.93   $189.95   $189.90  
  Purchase #5 $41.70   8.331%   $45.174   $45.17   $45.15   $45.20  
  Purchase #6 $149.37   13.442%   $169.4483   $169.45   $169.45   $169.40  
  Purchase #7 $203.61   7.246%   $218.3636   $218.36   $218.35   $218.40  
  7 purchase totals = $933.95       $1,012.4634   $1,012.45   $1,012.45   $1,012.40