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 $61.30   9.624%   $67.1995   $67.20   $67.20   $67.20  
  Purchase #2 $183.68   11.609%   $205.0034   $205.00   $205.00   $205.00  
  Purchase #3 $92.25   12.167%   $103.4741   $103.47   $103.45   $103.50  
  Purchase #4 $128.40   3.584%   $133.0019   $133.00   $133.00   $133.00  
  Purchase #5 $156.89   4.140%   $163.3852   $163.39   $163.40   $163.40  
  Purchase #6 $111.27   13.688%   $126.5006   $126.50   $126.50   $126.50  
  Purchase #7 $39.64   8.550%   $43.0292   $43.03   $43.05   $43.00  
  7 purchase totals = $773.43       $841.5939   $841.59   $841.60   $841.60