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 $187.59   9.855%   $206.077   $206.08   $206.10   $206.10  
  Purchase #2 $29.77   13.270%   $33.7205   $33.72   $33.70   $33.70  
  Purchase #3 $219.39   9.763%   $240.809   $240.81   $240.80   $240.80  
  Purchase #4 $181.37   11.775%   $202.7263   $202.73   $202.75   $202.70  
  Purchase #5 $51.63   8.202%   $55.8647   $55.86   $55.85   $55.90  
  Purchase #6 $248.93   5.255%   $262.0113   $262.01   $262.00   $262.00  
  Purchase #7 $216.48   12.398%   $243.3192   $243.32   $243.30   $243.30  
  7 purchase totals = $1,135.16       $1,244.5280   $1,244.53   $1,244.50   $1,244.50