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 $60.48   6.623%   $64.4856   $64.49   $64.50   $64.50  
  Purchase #2 $160.89   13.135%   $182.0229   $182.02   $182.00   $182.00  
  Purchase #3 $242.91   3.115%   $250.4766   $250.48   $250.50   $250.50  
  Purchase #4 $247.45   5.423%   $260.8692   $260.87   $260.85   $260.90  
  Purchase #5 $103.32   10.148%   $113.8049   $113.80   $113.80   $113.80  
  Purchase #6 $147.36   6.779%   $157.3495   $157.35   $157.35   $157.30  
  Purchase #7 $86.50   5.807%   $91.5231   $91.52   $91.50   $91.50  
  7 purchase totals = $1,048.91       $1,120.5318   $1,120.53   $1,120.50   $1,120.50