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 $150.86   11.378%   $168.0249   $168.02   $168.00   $168.00  
  Purchase #2 $54.96   8.631%   $59.7036   $59.70   $59.70   $59.70  
  Purchase #3 $16.75   4.723%   $17.5411   $17.54   $17.55   $17.50  
  Purchase #4 $165.78   6.384%   $176.3634   $176.36   $176.35   $176.40  
  Purchase #5 $140.28   11.358%   $156.213   $156.21   $156.20   $156.20  
  Purchase #6 $137.54   8.678%   $149.4757   $149.48   $149.50   $149.50  
  Purchase #7 $120.60   11.399%   $134.3472   $134.35   $134.35   $134.30  
  7 purchase totals = $786.77       $861.6689   $861.66   $861.65   $861.60