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 $131.84   11.680%   $147.2389   $147.24   $147.25   $147.20  
  Purchase #2 $57.53   5.782%   $60.8564   $60.86   $60.85   $60.90  
  Purchase #3 $10.41   13.584%   $11.8241   $11.82   $11.80   $11.80  
  Purchase #4 $165.84   3.371%   $171.4305   $171.43   $171.45   $171.40  
  Purchase #5 $89.43   8.151%   $96.7194   $96.72   $96.70   $96.70  
  Purchase #6 $51.91   12.362%   $58.3271   $58.33   $58.35   $58.30  
  Purchase #7 $212.47   3.372%   $219.6345   $219.63   $219.65   $219.60  
  7 purchase totals = $719.43       $766.0309   $766.03   $766.05   $765.90