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 $65.59   5.138%   $68.96   $68.96   $68.95   $69.00  
  Purchase #2 $173.32   7.375%   $186.1024   $186.10   $186.10   $186.10  
  Purchase #3 $243.81   3.617%   $252.6286   $252.63   $252.65   $252.60  
  Purchase #4 $34.57   9.734%   $37.935   $37.94   $37.95   $37.90  
  Purchase #5 $238.59   5.482%   $251.6695   $251.67   $251.65   $251.70  
  Purchase #6 $72.29   13.381%   $81.9631   $81.96   $81.95   $82.00  
  Purchase #7 $46.73   12.370%   $52.5105   $52.51   $52.50   $52.50  
  7 purchase totals = $874.90       $931.7691   $931.77   $931.75   $931.80