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 $51.37   9.450%   $56.2245   $56.22   $56.20   $56.20  
  Purchase #2 $167.49   4.573%   $175.1493   $175.15   $175.15   $175.10  
  Purchase #3 $165.90   10.347%   $183.0657   $183.07   $183.05   $183.10  
  Purchase #4 $108.98   5.788%   $115.2878   $115.29   $115.30   $115.30  
  Purchase #5 $91.57   11.411%   $102.0191   $102.02   $102.00   $102.00  
  Purchase #6 $137.68   4.594%   $144.005   $144.01   $144.00   $144.00  
  Purchase #7 $235.98   12.757%   $266.084   $266.08   $266.10   $266.10  
  7 purchase totals = $958.97       $1,041.8354   $1,041.84   $1,041.80   $1,041.80