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 $128.56   10.207%   $141.6821   $141.68   $141.70   $141.70  
  Purchase #2 $192.41   12.177%   $215.8398   $215.84   $215.85   $215.80  
  Purchase #3 $44.65   12.663%   $50.304   $50.30   $50.30   $50.30  
  Purchase #4 $25.35   4.781%   $26.562   $26.56   $26.55   $26.60  
  Purchase #5 $63.26   11.660%   $70.6361   $70.64   $70.65   $70.60  
  Purchase #6 $114.25   9.248%   $124.8158   $124.82   $124.80   $124.80  
  Purchase #7 $228.40   3.764%   $236.997   $237.00   $237.00   $237.00  
  7 purchase totals = $796.88       $866.8368   $866.84   $866.85   $866.80