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 $44.82   8.658%   $48.7005   $48.70   $48.70   $48.70  
  Purchase #2 $227.54   11.269%   $253.1815   $253.18   $253.20   $253.20  
  Purchase #3 $159.26   7.418%   $171.0739   $171.07   $171.05   $171.10  
  Purchase #4 $183.58   11.207%   $204.1538   $204.15   $204.15   $204.20  
  Purchase #5 $161.60   6.554%   $172.1913   $172.19   $172.20   $172.20  
  Purchase #6 $244.84   6.615%   $261.0362   $261.04   $261.05   $261.00  
  Purchase #7 $183.47   3.154%   $189.2566   $189.26   $189.25   $189.30  
  7 purchase totals = $1,205.11       $1,299.5938   $1,299.59   $1,299.60   $1,299.70