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 $202.36   10.458%   $223.5228   $223.52   $223.50   $223.50  
  Purchase #2 $161.96   12.176%   $181.6802   $181.68   $181.70   $181.70  
  Purchase #3 $5.91   9.264%   $6.4575   $6.46   $6.45   $6.50  
  Purchase #4 $205.81   7.657%   $221.5689   $221.57   $221.55   $221.60  
  Purchase #5 $33.66   9.519%   $36.8641   $36.86   $36.85   $36.90  
  Purchase #6 $65.75   4.503%   $68.7107   $68.71   $68.70   $68.70  
  Purchase #7 $124.37   13.570%   $141.247   $141.25   $141.25   $141.20  
  7 purchase totals = $799.82       $880.0512   $880.05   $880.00   $880.10