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 $54.95   12.639%   $61.8951   $61.90   $61.90   $61.90  
  Purchase #2 $173.90   6.718%   $185.5826   $185.58   $185.60   $185.60  
  Purchase #3 $182.51   8.305%   $197.6675   $197.67   $197.65   $197.70  
  Purchase #4 $41.99   8.510%   $45.5633   $45.56   $45.55   $45.60  
  Purchase #5 $234.38   5.175%   $246.5092   $246.51   $246.50   $246.50  
  Purchase #6 $56.99   6.458%   $60.6704   $60.67   $60.65   $60.70  
  Purchase #7 $48.42   13.450%   $54.9325   $54.93   $54.95   $54.90  
  7 purchase totals = $793.14       $852.8206   $852.82   $852.80   $852.90