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 $188.77   6.715%   $201.4459   $201.45   $201.45   $201.40  
  Purchase #2 $51.83   8.405%   $56.1863   $56.19   $56.20   $56.20  
  Purchase #3 $166.79   4.704%   $174.6358   $174.64   $174.65   $174.60  
  Purchase #4 $45.62   9.650%   $50.0223   $50.02   $50.00   $50.00  
  Purchase #5 $104.45   5.221%   $109.9033   $109.90   $109.90   $109.90  
  Purchase #6 $78.37   8.808%   $85.2728   $85.27   $85.25   $85.30  
  Purchase #7 $106.84   10.446%   $118.0005   $118.00   $118.00   $118.00  
  7 purchase totals = $742.67       $795.4669   $795.47   $795.45   $795.40