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 $216.38   4.461%   $226.0327   $226.03   $226.05   $226.00  
  Purchase #2 $228.69   9.460%   $250.3241   $250.32   $250.30   $250.30  
  Purchase #3 $49.95   13.687%   $56.7867   $56.79   $56.80   $56.80  
  Purchase #4 $169.36   11.817%   $189.3733   $189.37   $189.35   $189.40  
  Purchase #5 $153.60   9.405%   $168.0461   $168.05   $168.05   $168.00  
  Purchase #6 $74.93   6.512%   $79.8094   $79.81   $79.80   $79.80  
  Purchase #7 $91.48   3.264%   $94.4659   $94.47   $94.45   $94.50  
  7 purchase totals = $984.39       $1,064.8382   $1,064.84   $1,064.80   $1,064.80