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 $46.93   7.564%   $50.4798   $50.48   $50.50   $50.50  
  Purchase #2 $154.95   11.219%   $172.3338   $172.33   $172.35   $172.30  
  Purchase #3 $180.64   12.731%   $203.6373   $203.64   $203.65   $203.60  
  Purchase #4 $71.79   8.387%   $77.811   $77.81   $77.80   $77.80  
  Purchase #5 $195.96   6.460%   $208.619   $208.62   $208.60   $208.60  
  Purchase #6 $164.66   4.143%   $171.4819   $171.48   $171.50   $171.50  
  Purchase #7 $58.52   4.569%   $61.1938   $61.19   $61.20   $61.20  
  7 purchase totals = $873.45       $945.5566   $945.55   $945.60   $945.50