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 $149.83   9.648%   $164.2856   $164.29   $164.30   $164.30  
  Purchase #2 $191.43   4.820%   $200.6569   $200.66   $200.65   $200.70  
  Purchase #3 $103.65   9.371%   $113.363   $113.36   $113.35   $113.40  
  Purchase #4 $162.26   12.401%   $182.3819   $182.38   $182.40   $182.40  
  Purchase #5 $49.95   6.452%   $53.1728   $53.17   $53.15   $53.20  
  Purchase #6 $210.94   8.319%   $228.4881   $228.49   $228.50   $228.50  
  Purchase #7 $92.90   4.445%   $97.0294   $97.03   $97.05   $97.00  
  7 purchase totals = $960.96       $1,039.3777   $1,039.38   $1,039.40   $1,039.50