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 $64.58   3.755%   $67.005   $67.01   $67.00   $67.00  
  Purchase #2 $163.76   9.202%   $178.8292   $178.83   $178.85   $178.80  
  Purchase #3 $174.88   3.308%   $180.665   $180.67   $180.65   $180.70  
  Purchase #4 $15.60   12.443%   $17.5411   $17.54   $17.55   $17.50  
  Purchase #5 $164.43   10.202%   $181.2051   $181.21   $181.20   $181.20  
  Purchase #6 $138.94   8.218%   $150.3581   $150.36   $150.35   $150.40  
  Purchase #7 $155.32   11.631%   $173.3853   $173.39   $173.40   $173.40  
  7 purchase totals = $877.51       $948.9888   $949.01   $949.00   $949.00