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 $27.94   5.676%   $29.5259   $29.53   $29.55   $29.50  
  Purchase #2 $165.75   9.713%   $181.8493   $181.85   $181.85   $181.80  
  Purchase #3 $96.78   13.811%   $110.1463   $110.15   $110.15   $110.10  
  Purchase #4 $45.76   13.334%   $51.8616   $51.86   $51.85   $51.90  
  Purchase #5 $195.30   11.527%   $217.8122   $217.81   $217.80   $217.80  
  Purchase #6 $71.75   12.737%   $80.8888   $80.89   $80.90   $80.90  
  Purchase #7 $212.98   3.729%   $220.922   $220.92   $220.90   $220.90  
  7 purchase totals = $816.26       $893.0061   $893.01   $893.00   $892.90