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 $208.46   13.518%   $236.6396   $236.64   $236.65   $236.60  
  Purchase #2 $220.69   10.550%   $243.9728   $243.97   $243.95   $244.00  
  Purchase #3 $87.72   13.630%   $99.6762   $99.68   $99.70   $99.70  
  Purchase #4 $7.55   3.579%   $7.8202   $7.82   $7.80   $7.80  
  Purchase #5 $28.28   11.711%   $31.5919   $31.59   $31.60   $31.60  
  Purchase #6 $211.25   9.257%   $230.8054   $230.81   $230.80   $230.80  
  Purchase #7 $190.49   12.588%   $214.4689   $214.47   $214.45   $214.50  
  7 purchase totals = $954.44       $1,064.9750   $1,064.98   $1,064.95   $1,065.00