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 $193.98   11.731%   $216.7358   $216.74   $216.75   $216.70  
  Purchase #2 $143.85   4.838%   $150.8095   $150.81   $150.80   $150.80  
  Purchase #3 $10.36   10.133%   $11.4098   $11.41   $11.40   $11.40  
  Purchase #4 $207.78   12.653%   $234.0704   $234.07   $234.05   $234.10  
  Purchase #5 $111.48   11.547%   $124.3526   $124.35   $124.35   $124.40  
  Purchase #6 $25.45   3.655%   $26.3802   $26.38   $26.40   $26.40  
  Purchase #7 $167.49   3.424%   $173.2249   $173.22   $173.20   $173.20  
  7 purchase totals = $860.39       $936.9832   $936.98   $936.95   $937.00