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 $232.51   5.862%   $246.1397   $246.14   $246.15   $246.10  
  Purchase #2 $53.81   3.349%   $55.6121   $55.61   $55.60   $55.60  
  Purchase #3 $201.76   7.874%   $217.6466   $217.65   $217.65   $217.60  
  Purchase #4 $31.29   11.443%   $34.8705   $34.87   $34.85   $34.90  
  Purchase #5 $70.35   5.847%   $74.4634   $74.46   $74.45   $74.50  
  Purchase #6 $160.26   4.799%   $167.9509   $167.95   $167.95   $168.00  
  Purchase #7 $111.56   5.200%   $117.3611   $117.36   $117.35   $117.40  
  7 purchase totals = $861.54       $914.0443   $914.04   $914.00   $914.10