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 $54.91   7.806%   $59.1963   $59.20   $59.20   $59.20  
  Purchase #2 $175.58   6.703%   $187.3491   $187.35   $187.35   $187.30  
  Purchase #3 $47.56   3.239%   $49.1005   $49.10   $49.10   $49.10  
  Purchase #4 $135.54   12.567%   $152.5733   $152.57   $152.55   $152.60  
  Purchase #5 $233.68   11.366%   $260.2401   $260.24   $260.25   $260.20  
  Purchase #6 $144.98   10.349%   $159.984   $159.98   $160.00   $160.00  
  Purchase #7 $241.34   7.207%   $258.7334   $258.73   $258.75   $258.70  
  7 purchase totals = $1,033.59       $1,127.1767   $1,127.17   $1,127.20   $1,127.10