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 $108.70   6.314%   $115.5633   $115.56   $115.55   $115.60  
  Purchase #2 $196.34   3.427%   $203.0686   $203.07   $203.05   $203.10  
  Purchase #3 $124.95   6.373%   $132.9131   $132.91   $132.90   $132.90  
  Purchase #4 $123.44   9.439%   $135.0915   $135.09   $135.10   $135.10  
  Purchase #5 $138.66   12.535%   $156.041   $156.04   $156.05   $156.00  
  Purchase #6 $235.36   3.456%   $243.494   $243.49   $243.50   $243.50  
  Purchase #7 $70.78   5.553%   $74.7104   $74.71   $74.70   $74.70  
  7 purchase totals = $998.23       $1,060.8819   $1,060.87   $1,060.85   $1,060.90