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 $47.37   4.794%   $49.6409   $49.64   $49.65   $49.60  
  Purchase #2 $120.35   13.213%   $136.2518   $136.25   $136.25   $136.30  
  Purchase #3 $231.31   8.304%   $250.518   $250.52   $250.50   $250.50  
  Purchase #4 $63.98   4.281%   $66.719   $66.72   $66.70   $66.70  
  Purchase #5 $201.76   11.702%   $225.37   $225.37   $225.35   $225.40  
  Purchase #6 $167.80   3.573%   $173.7955   $173.80   $173.80   $173.80  
  Purchase #7 $38.27   10.180%   $42.1659   $42.17   $42.15   $42.20  
  7 purchase totals = $870.84       $944.4611   $944.47   $944.40   $944.50