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 $60.33   7.257%   $64.7081   $64.71   $64.70   $64.70  
  Purchase #2 $108.57   13.129%   $122.8242   $122.82   $122.80   $122.80  
  Purchase #3 $241.28   8.679%   $262.2207   $262.22   $262.20   $262.20  
  Purchase #4 $195.34   4.785%   $204.687   $204.69   $204.70   $204.70  
  Purchase #5 $50.43   13.183%   $57.0782   $57.08   $57.10   $57.10  
  Purchase #6 $128.84   13.616%   $146.3829   $146.38   $146.40   $146.40  
  Purchase #7 $172.98   8.244%   $187.2405   $187.24   $187.25   $187.20  
  7 purchase totals = $957.77       $1,045.1416   $1,045.14   $1,045.15   $1,045.10