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 $199.91   8.751%   $217.4041   $217.40   $217.40   $217.40  
  Purchase #2 $207.47   5.592%   $219.0717   $219.07   $219.05   $219.10  
  Purchase #3 $113.67   6.571%   $121.1393   $121.14   $121.15   $121.10  
  Purchase #4 $36.26   9.372%   $39.6583   $39.66   $39.65   $39.70  
  Purchase #5 $222.53   13.322%   $252.1754   $252.18   $252.20   $252.20  
  Purchase #6 $208.49   5.452%   $219.8569   $219.86   $219.85   $219.90  
  Purchase #7 $77.67   12.376%   $87.2824   $87.28   $87.30   $87.30  
  7 purchase totals = $1,066.00       $1,156.5881   $1,156.59   $1,156.60   $1,156.70