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 $55.49   11.280%   $61.7493   $61.75   $61.75   $61.70  
  Purchase #2 $244.28   8.358%   $264.6969   $264.70   $264.70   $264.70  
  Purchase #3 $152.70   11.160%   $169.7413   $169.74   $169.75   $169.70  
  Purchase #4 $11.45   4.737%   $11.9924   $11.99   $12.00   $12.00  
  Purchase #5 $113.86   5.385%   $119.9914   $119.99   $120.00   $120.00  
  Purchase #6 $40.91   12.368%   $45.9697   $45.97   $45.95   $46.00  
  Purchase #7 $120.86   8.522%   $131.1597   $131.16   $131.15   $131.20  
  7 purchase totals = $739.55       $805.3007   $805.30   $805.30   $805.30