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 $33.52   12.531%   $37.7204   $37.72   $37.70   $37.70  
  Purchase #2 $201.31   11.269%   $223.9956   $224.00   $224.00   $224.00  
  Purchase #3 $15.49   9.128%   $16.9039   $16.90   $16.90   $16.90  
  Purchase #4 $246.40   12.518%   $277.2444   $277.24   $277.25   $277.20  
  Purchase #5 $236.27   9.817%   $259.4646   $259.46   $259.45   $259.50  
  Purchase #6 $62.53   12.542%   $70.3725   $70.37   $70.35   $70.40  
  Purchase #7 $195.94   6.332%   $208.3469   $208.35   $208.35   $208.30  
  7 purchase totals = $991.46       $1,094.0483   $1,094.04   $1,094.00   $1,094.00