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 $205.62   3.236%   $212.2739   $212.27   $212.25   $212.30  
  Purchase #2 $174.43   10.463%   $192.6806   $192.68   $192.70   $192.70  
  Purchase #3 $155.70   13.573%   $176.8332   $176.83   $176.85   $176.80  
  Purchase #4 $26.79   7.439%   $28.7829   $28.78   $28.80   $28.80  
  Purchase #5 $140.84   3.436%   $145.6793   $145.68   $145.70   $145.70  
  Purchase #6 $188.50   6.645%   $201.0258   $201.03   $201.05   $201.00  
  Purchase #7 $16.58   6.560%   $17.6676   $17.67   $17.65   $17.70  
  7 purchase totals = $908.46       $974.9433   $974.94   $975.00   $975.00