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 $220.96   9.654%   $242.2915   $242.29   $242.30   $242.30  
  Purchase #2 $150.47   12.440%   $169.1885   $169.19   $169.20   $169.20  
  Purchase #3 $81.77   13.212%   $92.5735   $92.57   $92.55   $92.60  
  Purchase #4 $15.82   11.629%   $17.6597   $17.66   $17.65   $17.70  
  Purchase #5 $169.98   11.541%   $189.5974   $189.60   $189.60   $189.60  
  Purchase #6 $185.35   8.133%   $200.4245   $200.42   $200.40   $200.40  
  Purchase #7 $119.32   4.320%   $124.4746   $124.47   $124.45   $124.50  
  7 purchase totals = $943.67       $1,036.2097   $1,036.20   $1,036.15   $1,036.30