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 $168.96   10.356%   $186.4575   $186.46   $186.45   $186.50  
  Purchase #2 $160.45   9.659%   $175.9479   $175.95   $175.95   $175.90  
  Purchase #3 $186.89   6.277%   $198.6211   $198.62   $198.60   $198.60  
  Purchase #4 $132.41   4.107%   $137.8481   $137.85   $137.85   $137.80  
  Purchase #5 $58.80   6.551%   $62.652   $62.65   $62.65   $62.70  
  Purchase #6 $125.98   6.387%   $134.0263   $134.03   $134.05   $134.00  
  Purchase #7 $146.95   4.331%   $153.3144   $153.31   $153.30   $153.30  
  7 purchase totals = $980.44       $1,048.8673   $1,048.87   $1,048.85   $1,048.80