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 $222.86   8.151%   $241.0253   $241.03   $241.05   $241.00  
  Purchase #2 $250.96   9.557%   $274.9442   $274.94   $274.95   $274.90  
  Purchase #3 $50.60   8.656%   $54.9799   $54.98   $55.00   $55.00  
  Purchase #4 $165.51   8.373%   $179.3682   $179.37   $179.35   $179.40  
  Purchase #5 $158.67   5.701%   $167.7158   $167.72   $167.70   $167.70  
  Purchase #6 $154.82   12.667%   $174.431   $174.43   $174.45   $174.40  
  Purchase #7 $36.90   7.838%   $39.7922   $39.79   $39.80   $39.80  
  7 purchase totals = $1,040.32       $1,132.2566   $1,132.26   $1,132.30   $1,132.20