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 $164.74   13.870%   $187.5894   $187.59   $187.60   $187.60  
  Purchase #2 $231.28   9.371%   $252.9532   $252.95   $252.95   $253.00  
  Purchase #3 $205.67   8.864%   $223.9006   $223.90   $223.90   $223.90  
  Purchase #4 $216.28   7.297%   $232.062   $232.06   $232.05   $232.10  
  Purchase #5 $188.27   8.815%   $204.866   $204.87   $204.85   $204.90  
  Purchase #6 $212.34   13.791%   $241.6238   $241.62   $241.60   $241.60  
  Purchase #7 $60.38   8.222%   $65.3444   $65.34   $65.35   $65.30  
  7 purchase totals = $1,278.96       $1,408.3394   $1,408.33   $1,408.30   $1,408.40