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 $95.61   3.171%   $98.6418   $98.64   $98.65   $98.60  
  Purchase #2 $32.61   13.616%   $37.0502   $37.05   $37.05   $37.10  
  Purchase #3 $126.35   7.441%   $135.7517   $135.75   $135.75   $135.80  
  Purchase #4 $172.87   11.831%   $193.3222   $193.32   $193.30   $193.30  
  Purchase #5 $52.48   6.640%   $55.9647   $55.96   $55.95   $56.00  
  Purchase #6 $245.87   5.341%   $259.0019   $259.00   $259.00   $259.00  
  Purchase #7 $149.90   9.619%   $164.3189   $164.32   $164.30   $164.30  
  7 purchase totals = $875.69       $944.0514   $944.04   $944.00   $944.10