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 $58.99   6.199%   $62.6468   $62.65   $62.65   $62.60  
  Purchase #2 $70.31   13.473%   $79.7829   $79.78   $79.80   $79.80  
  Purchase #3 $147.70   12.810%   $166.6204   $166.62   $166.60   $166.60  
  Purchase #4 $239.56   4.697%   $250.8121   $250.81   $250.80   $250.80  
  Purchase #5 $199.94   8.364%   $216.663   $216.66   $216.65   $216.70  
  Purchase #6 $224.84   7.164%   $240.9475   $240.95   $240.95   $240.90  
  Purchase #7 $157.64   13.308%   $178.6187   $178.62   $178.60   $178.60  
  7 purchase totals = $1,098.98       $1,196.0914   $1,196.09   $1,196.05   $1,196.00