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 $32.90   12.663%   $37.0661   $37.07   $37.05   $37.10  
  Purchase #2 $184.54   4.770%   $193.3426   $193.34   $193.35   $193.30  
  Purchase #3 $90.70   9.250%   $99.0898   $99.09   $99.10   $99.10  
  Purchase #4 $228.60   10.260%   $252.0544   $252.05   $252.05   $252.10  
  Purchase #5 $60.43   5.179%   $63.5597   $63.56   $63.55   $63.60  
  Purchase #6 $232.57   6.765%   $248.3034   $248.30   $248.30   $248.30  
  Purchase #7 $127.87   4.321%   $133.3953   $133.40   $133.40   $133.40  
  7 purchase totals = $957.61       $1,026.8113   $1,026.81   $1,026.80   $1,026.90