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 $44.82   4.137%   $46.6742   $46.67   $46.65   $46.70  
  Purchase #2 $238.67   13.527%   $270.9549   $270.95   $270.95   $271.00  
  Purchase #3 $80.58   11.810%   $90.0965   $90.10   $90.10   $90.10  
  Purchase #4 $201.82   10.228%   $222.4621   $222.46   $222.45   $222.50  
  Purchase #5 $146.67   10.207%   $161.6406   $161.64   $161.65   $161.60  
  Purchase #6 $250.93   6.783%   $267.9506   $267.95   $267.95   $268.00  
  Purchase #7 $67.95   4.178%   $70.789   $70.79   $70.80   $70.80  
  7 purchase totals = $1,031.44       $1,130.5679   $1,130.56   $1,130.55   $1,130.70