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 $87.49   5.250%   $92.0832   $92.08   $92.10   $92.10  
  Purchase #2 $57.45   13.194%   $65.03   $65.03   $65.05   $65.00  
  Purchase #3 $198.43   5.563%   $209.4687   $209.47   $209.45   $209.50  
  Purchase #4 $196.49   4.376%   $205.0884   $205.09   $205.10   $205.10  
  Purchase #5 $67.29   11.435%   $74.9846   $74.98   $75.00   $75.00  
  Purchase #6 $33.69   11.857%   $37.6846   $37.68   $37.70   $37.70  
  Purchase #7 $153.26   11.463%   $170.8282   $170.83   $170.85   $170.80  
  7 purchase totals = $794.10       $855.1677   $855.16   $855.25   $855.20