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 $164.89   6.229%   $175.161   $175.16   $175.15   $175.20  
  Purchase #2 $231.34   5.759%   $244.6629   $244.66   $244.65   $244.70  
  Purchase #3 $149.54   4.789%   $156.7015   $156.70   $156.70   $156.70  
  Purchase #4 $118.65   8.181%   $128.3568   $128.36   $128.35   $128.40  
  Purchase #5 $57.99   11.418%   $64.6113   $64.61   $64.60   $64.60  
  Purchase #6 $203.83   7.109%   $218.3203   $218.32   $218.30   $218.30  
  Purchase #7 $27.65   11.347%   $30.7874   $30.79   $30.80   $30.80  
  7 purchase totals = $953.89       $1,018.6012   $1,018.60   $1,018.55   $1,018.70