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 $85.56   12.764%   $96.4809   $96.48   $96.50   $96.50  
  Purchase #2 $192.94   10.358%   $212.9247   $212.92   $212.90   $212.90  
  Purchase #3 $235.30   6.212%   $249.9168   $249.92   $249.90   $249.90  
  Purchase #4 $179.35   13.623%   $203.7829   $203.78   $203.80   $203.80  
  Purchase #5 $152.41   10.294%   $168.0991   $168.10   $168.10   $168.10  
  Purchase #6 $70.71   8.330%   $76.6001   $76.60   $76.60   $76.60  
  Purchase #7 $83.68   9.805%   $91.8848   $91.88   $91.90   $91.90  
  7 purchase totals = $999.95       $1,099.6893   $1,099.68   $1,099.70   $1,099.70