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 $68.33   7.626%   $73.5408   $73.54   $73.55   $73.50  
  Purchase #2 $147.28   12.163%   $165.1937   $165.19   $165.20   $165.20  
  Purchase #3 $230.47   9.384%   $252.0973   $252.10   $252.10   $252.10  
  Purchase #4 $108.46   11.510%   $120.9437   $120.94   $120.95   $120.90  
  Purchase #5 $174.33   4.544%   $182.2516   $182.25   $182.25   $182.30  
  Purchase #6 $25.78   11.500%   $28.7447   $28.74   $28.75   $28.70  
  Purchase #7 $229.69   7.138%   $246.0853   $246.09   $246.10   $246.10  
  7 purchase totals = $984.34       $1,068.8571   $1,068.85   $1,068.90   $1,068.80