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 $29.59   11.625%   $33.0298   $33.03   $33.05   $33.00  
  Purchase #2 $185.38   10.231%   $204.3462   $204.35   $204.35   $204.30  
  Purchase #3 $72.48   3.471%   $74.9958   $75.00   $75.00   $75.00  
  Purchase #4 $174.41   8.333%   $188.9436   $188.94   $188.95   $188.90  
  Purchase #5 $88.77   12.713%   $100.0553   $100.06   $100.05   $100.10  
  Purchase #6 $100.33   6.352%   $106.703   $106.70   $106.70   $106.70  
  Purchase #7 $223.78   8.209%   $242.1501   $242.15   $242.15   $242.20  
  7 purchase totals = $874.74       $950.2238   $950.23   $950.25   $950.20