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 $50.83   9.663%   $55.7417   $55.74   $55.75   $55.70  
  Purchase #2 $242.61   11.105%   $269.5518   $269.55   $269.55   $269.60  
  Purchase #3 $203.43   3.198%   $209.9357   $209.94   $209.95   $209.90  
  Purchase #4 $121.51   11.288%   $135.226   $135.23   $135.25   $135.20  
  Purchase #5 $8.53   4.164%   $8.8852   $8.89   $8.90   $8.90  
  Purchase #6 $183.70   8.186%   $198.7377   $198.74   $198.75   $198.70  
  Purchase #7 $134.52   9.711%   $147.5832   $147.58   $147.60   $147.60  
  7 purchase totals = $945.13       $1,025.6613   $1,025.67   $1,025.75   $1,025.60