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 $50.99   13.472%   $57.8594   $57.86   $57.85   $57.90  
  Purchase #2 $174.63   9.146%   $190.6017   $190.60   $190.60   $190.60  
  Purchase #3 $157.95   7.166%   $169.2687   $169.27   $169.25   $169.30  
  Purchase #4 $50.55   6.227%   $53.6977   $53.70   $53.70   $53.70  
  Purchase #5 $107.79   13.375%   $122.2069   $122.21   $122.20   $122.20  
  Purchase #6 $241.35   5.289%   $254.115   $254.12   $254.10   $254.10  
  Purchase #7 $241.33   11.645%   $269.4329   $269.43   $269.45   $269.40  
  7 purchase totals = $1,024.59       $1,117.1823   $1,117.19   $1,117.15   $1,117.20