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 $88.59   11.367%   $98.66   $98.66   $98.65   $98.70  
  Purchase #2 $36.67   8.157%   $39.6612   $39.66   $39.65   $39.70  
  Purchase #3 $103.40   9.309%   $113.0255   $113.03   $113.05   $113.00  
  Purchase #4 $55.86   12.107%   $62.623   $62.62   $62.60   $62.60  
  Purchase #5 $182.76   7.114%   $195.7615   $195.76   $195.75   $195.80  
  Purchase #6 $46.52   3.173%   $47.9961   $48.00   $48.00   $48.00  
  Purchase #7 $129.55   4.152%   $134.9289   $134.93   $134.95   $134.90  
  7 purchase totals = $643.35       $692.6562   $692.66   $692.65   $692.70