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 $54.33   13.291%   $61.551   $61.55   $61.55   $61.60  
  Purchase #2 $202.47   3.828%   $210.2206   $210.22   $210.20   $210.20  
  Purchase #3 $131.94   8.417%   $143.0454   $143.05   $143.05   $143.00  
  Purchase #4 $246.43   9.376%   $269.5353   $269.54   $269.55   $269.50  
  Purchase #5 $190.81   13.802%   $217.1456   $217.15   $217.15   $217.10  
  Purchase #6 $149.55   13.318%   $169.4671   $169.47   $169.45   $169.50  
  Purchase #7 $229.91   11.347%   $255.9979   $256.00   $256.00   $256.00  
  7 purchase totals = $1,205.44       $1,326.9629   $1,326.98   $1,326.95   $1,326.90