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 $34.51   11.433%   $38.4555   $38.46   $38.45   $38.50  
  Purchase #2 $55.62   9.194%   $60.7337   $60.73   $60.75   $60.70  
  Purchase #3 $162.96   11.644%   $181.9351   $181.94   $181.95   $181.90  
  Purchase #4 $92.39   6.274%   $98.1865   $98.19   $98.20   $98.20  
  Purchase #5 $202.89   3.484%   $209.9587   $209.96   $209.95   $210.00  
  Purchase #6 $225.42   3.375%   $233.0279   $233.03   $233.05   $233.00  
  Purchase #7 $235.77   7.462%   $253.3632   $253.36   $253.35   $253.40  
  7 purchase totals = $1,009.56       $1,075.6606   $1,075.67   $1,075.70   $1,075.70