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 $61.96   9.619%   $67.9199   $67.92   $67.90   $67.90  
  Purchase #2 $32.33   8.198%   $34.9804   $34.98   $35.00   $35.00  
  Purchase #3 $92.50   8.130%   $100.0203   $100.02   $100.00   $100.00  
  Purchase #4 $58.95   9.671%   $64.6511   $64.65   $64.65   $64.70  
  Purchase #5 $12.30   6.855%   $13.1432   $13.14   $13.15   $13.10  
  Purchase #6 $93.85   6.304%   $99.7663   $99.77   $99.75   $99.80  
  Purchase #7 $109.80   10.728%   $121.5793   $121.58   $121.60   $121.60  
  7 purchase totals = $461.69       $502.0605   $502.06   $502.05   $502.10