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 $230.42   11.545%   $257.022   $257.02   $257.00   $257.00  
  Purchase #2 $12.57   7.513%   $13.5144   $13.51   $13.50   $13.50  
  Purchase #3 $216.75   6.155%   $230.091   $230.09   $230.10   $230.10  
  Purchase #4 $174.64   8.499%   $189.4827   $189.48   $189.50   $189.50  
  Purchase #5 $115.69   13.472%   $131.2758   $131.28   $131.30   $131.30  
  Purchase #6 $104.93   7.368%   $112.6612   $112.66   $112.65   $112.70  
  Purchase #7 $120.64   4.802%   $126.4331   $126.43   $126.45   $126.40  
  7 purchase totals = $975.64       $1,060.4802   $1,060.47   $1,060.50   $1,060.50