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 $248.92   3.631%   $257.9583   $257.96   $257.95   $258.00  
  Purchase #2 $152.67   7.413%   $163.9874   $163.99   $164.00   $164.00  
  Purchase #3 $227.32   7.819%   $245.0942   $245.09   $245.10   $245.10  
  Purchase #4 $148.28   11.698%   $165.6258   $165.63   $165.65   $165.60  
  Purchase #5 $87.62   9.501%   $95.9448   $95.94   $95.95   $95.90  
  Purchase #6 $52.38   7.142%   $56.121   $56.12   $56.10   $56.10  
  Purchase #7 $102.27   8.855%   $111.326   $111.33   $111.35   $111.30  
  7 purchase totals = $1,019.46       $1,096.0575   $1,096.06   $1,096.10   $1,096.00