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 $61.40   11.177%   $68.2627   $68.26   $68.25   $68.30  
  Purchase #2 $184.92   7.667%   $199.0978   $199.10   $199.10   $199.10  
  Purchase #3 $202.95   7.332%   $217.8303   $217.83   $217.85   $217.80  
  Purchase #4 $134.41   6.751%   $143.484   $143.48   $143.50   $143.50  
  Purchase #5 $39.29   8.644%   $42.6862   $42.69   $42.70   $42.70  
  Purchase #6 $163.67   7.772%   $176.3904   $176.39   $176.40   $176.40  
  Purchase #7 $44.60   9.364%   $48.7763   $48.78   $48.80   $48.80  
  7 purchase totals = $831.24       $896.5277   $896.53   $896.60   $896.60