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 $130.80   6.672%   $139.527   $139.53   $139.55   $139.50  
  Purchase #2 $153.68   4.158%   $160.07   $160.07   $160.05   $160.10  
  Purchase #3 $210.42   3.654%   $218.1087   $218.11   $218.10   $218.10  
  Purchase #4 $59.93   5.617%   $63.2963   $63.30   $63.30   $63.30  
  Purchase #5 $171.42   9.650%   $187.962   $187.96   $187.95   $188.00  
  Purchase #6 $74.58   13.427%   $84.5939   $84.59   $84.60   $84.60  
  Purchase #7 $218.62   10.669%   $241.9446   $241.94   $241.95   $241.90  
  7 purchase totals = $1,019.45       $1,095.5025   $1,095.50   $1,095.50   $1,095.50