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 $174.66   9.461%   $191.1846   $191.18   $191.20   $191.20  
  Purchase #2 $195.41   13.389%   $221.5734   $221.57   $221.55   $221.60  
  Purchase #3 $32.85   12.128%   $36.834   $36.83   $36.85   $36.80  
  Purchase #4 $73.27   5.164%   $77.0537   $77.05   $77.05   $77.10  
  Purchase #5 $218.80   9.617%   $239.842   $239.84   $239.85   $239.80  
  Purchase #6 $130.26   11.597%   $145.3663   $145.37   $145.35   $145.40  
  Purchase #7 $131.57   7.348%   $141.2378   $141.24   $141.25   $141.20  
  7 purchase totals = $956.82       $1,053.0918   $1,053.08   $1,053.10   $1,053.10