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 $187.60   8.751%   $204.0169   $204.02   $204.00   $204.00  
  Purchase #2 $198.55   7.461%   $213.3638   $213.36   $213.35   $213.40  
  Purchase #3 $93.57   4.774%   $98.037   $98.04   $98.05   $98.00  
  Purchase #4 $58.83   3.451%   $60.8602   $60.86   $60.85   $60.90  
  Purchase #5 $247.26   10.821%   $274.016   $274.02   $274.00   $274.00  
  Purchase #6 $63.28   13.242%   $71.6595   $71.66   $71.65   $71.70  
  Purchase #7 $180.65   5.790%   $191.1096   $191.11   $191.10   $191.10  
  7 purchase totals = $1,029.74       $1,113.0630   $1,113.07   $1,113.00   $1,113.10