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 $113.88   8.264%   $123.291   $123.29   $123.30   $123.30  
  Purchase #2 $181.31   8.835%   $197.3287   $197.33   $197.35   $197.30  
  Purchase #3 $126.99   5.435%   $133.8919   $133.89   $133.90   $133.90  
  Purchase #4 $144.58   8.596%   $157.0081   $157.01   $157.00   $157.00  
  Purchase #5 $13.94   7.284%   $14.9554   $14.96   $14.95   $15.00  
  Purchase #6 $205.67   13.679%   $233.8036   $233.80   $233.80   $233.80  
  Purchase #7 $33.71   4.701%   $35.2947   $35.29   $35.30   $35.30  
  7 purchase totals = $820.08       $895.5734   $895.57   $895.60   $895.60