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 $159.80   13.287%   $181.0326   $181.03   $181.05   $181.00  
  Purchase #2 $182.35   13.313%   $206.6263   $206.63   $206.65   $206.60  
  Purchase #3 $208.36   4.769%   $218.2967   $218.30   $218.30   $218.30  
  Purchase #4 $95.99   11.472%   $107.002   $107.00   $107.00   $107.00  
  Purchase #5 $116.28   12.418%   $130.7197   $130.72   $130.70   $130.70  
  Purchase #6 $184.71   4.274%   $192.6045   $192.60   $192.60   $192.60  
  Purchase #7 $211.52   9.144%   $230.8614   $230.86   $230.85   $230.90  
  7 purchase totals = $1,159.01       $1,267.1432   $1,267.14   $1,267.15   $1,267.10