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 $113.67   4.670%   $118.9784   $118.98   $119.00   $119.00  
  Purchase #2 $53.38   10.349%   $58.9043   $58.90   $58.90   $58.90  
  Purchase #3 $68.53   11.734%   $76.5713   $76.57   $76.55   $76.60  
  Purchase #4 $120.29   4.371%   $125.5479   $125.55   $125.55   $125.50  
  Purchase #5 $157.85   6.265%   $167.7393   $167.74   $167.75   $167.70  
  Purchase #6 $57.35   6.622%   $61.1477   $61.15   $61.15   $61.10  
  Purchase #7 $76.29   11.815%   $85.3037   $85.30   $85.30   $85.30  
  7 purchase totals = $647.36       $694.1926   $694.19   $694.20   $694.10