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 $169.95   13.270%   $192.5024   $192.50   $192.50   $192.50  
  Purchase #2 $98.31   6.402%   $104.6038   $104.60   $104.60   $104.60  
  Purchase #3 $59.60   5.797%   $63.055   $63.06   $63.05   $63.10  
  Purchase #4 $201.59   6.410%   $214.5119   $214.51   $214.50   $214.50  
  Purchase #5 $80.43   8.851%   $87.5489   $87.55   $87.55   $87.50  
  Purchase #6 $28.25   11.180%   $31.4084   $31.41   $31.40   $31.40  
  Purchase #7 $99.49   3.718%   $103.189   $103.19   $103.20   $103.20  
  7 purchase totals = $737.62       $796.8194   $796.82   $796.80   $796.80