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 $91.93   12.133%   $103.0839   $103.08   $103.10   $103.10  
  Purchase #2 $181.88   7.509%   $195.5374   $195.54   $195.55   $195.50  
  Purchase #3 $189.28   8.171%   $204.7461   $204.75   $204.75   $204.70  
  Purchase #4 $14.68   13.573%   $16.6725   $16.67   $16.65   $16.70  
  Purchase #5 $157.54   12.554%   $177.3176   $177.32   $177.30   $177.30  
  Purchase #6 $118.93   3.633%   $123.2507   $123.25   $123.25   $123.30  
  Purchase #7 $79.89   13.838%   $90.9452   $90.95   $90.95   $90.90  
  7 purchase totals = $834.13       $911.5534   $911.56   $911.55   $911.50