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 $111.29   13.269%   $126.0571   $126.06   $126.05   $126.10  
  Purchase #2 $162.56   7.402%   $174.5927   $174.59   $174.60   $174.60  
  Purchase #3 $218.57   5.516%   $230.6263   $230.63   $230.65   $230.60  
  Purchase #4 $37.55   5.386%   $39.5724   $39.57   $39.55   $39.60  
  Purchase #5 $240.57   7.113%   $257.6817   $257.68   $257.70   $257.70  
  Purchase #6 $53.63   3.401%   $55.454   $55.45   $55.45   $55.50  
  Purchase #7 $164.54   13.366%   $186.5324   $186.53   $186.55   $186.50  
  7 purchase totals = $988.71       $1,070.5166   $1,070.51   $1,070.55   $1,070.60