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 $61.44   6.676%   $65.5417   $65.54   $65.55   $65.50  
  Purchase #2 $239.63   4.851%   $251.2545   $251.25   $251.25   $251.30  
  Purchase #3 $76.88   3.605%   $79.6515   $79.65   $79.65   $79.70  
  Purchase #4 $244.31   13.552%   $277.4189   $277.42   $277.40   $277.40  
  Purchase #5 $170.48   9.185%   $186.1386   $186.14   $186.15   $186.10  
  Purchase #6 $172.41   3.570%   $178.565   $178.57   $178.55   $178.60  
  Purchase #7 $55.70   12.790%   $62.824   $62.82   $62.80   $62.80  
  7 purchase totals = $1,020.85       $1,101.3942   $1,101.39   $1,101.35   $1,101.40