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 $68.39   9.502%   $74.8884   $74.89   $74.90   $74.90  
  Purchase #2 $110.38   3.869%   $114.6506   $114.65   $114.65   $114.70  
  Purchase #3 $88.95   10.154%   $97.982   $97.98   $98.00   $98.00  
  Purchase #4 $189.69   7.452%   $203.8257   $203.83   $203.85   $203.80  
  Purchase #5 $212.36   5.611%   $224.2755   $224.28   $224.30   $224.30  
  Purchase #6 $143.72   10.404%   $158.6726   $158.67   $158.65   $158.70  
  Purchase #7 $129.25   13.755%   $147.0283   $147.03   $147.05   $147.00  
  7 purchase totals = $942.74       $1,021.3231   $1,021.33   $1,021.40   $1,021.40