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 $104.48   5.324%   $110.0425   $110.04   $110.05   $110.00  
  Purchase #2 $58.40   4.174%   $60.8376   $60.84   $60.85   $60.80  
  Purchase #3 $193.81   4.614%   $202.7524   $202.75   $202.75   $202.80  
  Purchase #4 $125.89   4.202%   $131.1799   $131.18   $131.20   $131.20  
  Purchase #5 $152.28   13.644%   $173.0571   $173.06   $173.05   $173.10  
  Purchase #6 $168.99   3.812%   $175.4319   $175.43   $175.45   $175.40  
  Purchase #7 $192.57   9.619%   $211.0933   $211.09   $211.10   $211.10  
  7 purchase totals = $996.42       $1,064.3947   $1,064.39   $1,064.45   $1,064.40