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 $54.81   6.168%   $58.1907   $58.19   $58.20   $58.20  
  Purchase #2 $113.80   11.282%   $126.6389   $126.64   $126.65   $126.60  
  Purchase #3 $129.96   5.575%   $137.2053   $137.21   $137.20   $137.20  
  Purchase #4 $139.66   4.213%   $145.5439   $145.54   $145.55   $145.50  
  Purchase #5 $44.28   7.643%   $47.6643   $47.66   $47.65   $47.70  
  Purchase #6 $234.62   7.623%   $252.5051   $252.51   $252.50   $252.50  
  Purchase #7 $228.80   4.429%   $238.9336   $238.93   $238.95   $238.90  
  7 purchase totals = $945.93       $1,006.6818   $1,006.68   $1,006.70   $1,006.60