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 $150.93   10.645%   $166.9965   $167.00   $167.00   $167.00  
  Purchase #2 $58.61   13.815%   $66.707   $66.71   $66.70   $66.70  
  Purchase #3 $194.72   13.473%   $220.9546   $220.95   $220.95   $221.00  
  Purchase #4 $52.80   7.135%   $56.5673   $56.57   $56.55   $56.60  
  Purchase #5 $190.55   5.349%   $200.7425   $200.74   $200.75   $200.70  
  Purchase #6 $165.62   10.616%   $183.2022   $183.20   $183.20   $183.20  
  Purchase #7 $106.91   11.261%   $118.9491   $118.95   $118.95   $118.90  
  7 purchase totals = $920.14       $1,014.1192   $1,014.12   $1,014.10   $1,014.10