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 $177.57   11.596%   $198.161   $198.16   $198.15   $198.20  
  Purchase #2 $211.64   7.113%   $226.694   $226.69   $226.70   $226.70  
  Purchase #3 $118.75   5.382%   $125.1411   $125.14   $125.15   $125.10  
  Purchase #4 $128.85   4.162%   $134.2127   $134.21   $134.20   $134.20  
  Purchase #5 $190.99   6.198%   $202.8276   $202.83   $202.85   $202.80  
  Purchase #6 $110.51   7.634%   $118.9463   $118.95   $118.95   $118.90  
  Purchase #7 $199.74   11.635%   $222.9797   $222.98   $223.00   $223.00  
  7 purchase totals = $1,138.05       $1,228.9624   $1,228.96   $1,229.00   $1,228.90