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 $104.31   6.655%   $111.2518   $111.25   $111.25   $111.30  
  Purchase #2 $170.99   7.525%   $183.857   $183.86   $183.85   $183.90  
  Purchase #3 $117.69   4.842%   $123.3885   $123.39   $123.40   $123.40  
  Purchase #4 $159.42   8.495%   $172.9627   $172.96   $172.95   $173.00  
  Purchase #5 $58.40   9.560%   $63.983   $63.98   $64.00   $64.00  
  Purchase #6 $18.91   13.791%   $21.5179   $21.52   $21.50   $21.50  
  Purchase #7 $14.73   9.311%   $16.1015   $16.10   $16.10   $16.10  
  7 purchase totals = $644.45       $693.0624   $693.06   $693.05   $693.20