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 $238.38   8.737%   $259.2073   $259.21   $259.20   $259.20  
  Purchase #2 $212.34   13.343%   $240.6725   $240.67   $240.65   $240.70  
  Purchase #3 $114.85   11.622%   $128.1979   $128.20   $128.20   $128.20  
  Purchase #4 $97.91   9.149%   $106.8678   $106.87   $106.85   $106.90  
  Purchase #5 $213.69   12.771%   $240.9803   $240.98   $241.00   $241.00  
  Purchase #6 $120.87   9.583%   $132.453   $132.45   $132.45   $132.50  
  Purchase #7 $223.95   6.458%   $238.4127   $238.41   $238.40   $238.40  
  7 purchase totals = $1,221.99       $1,346.7915   $1,346.79   $1,346.75   $1,346.90