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 $46.54   7.436%   $50.0007   $50.00   $50.00   $50.00  
  Purchase #2 $193.94   10.602%   $214.5015   $214.50   $214.50   $214.50  
  Purchase #3 $84.31   4.782%   $88.3417   $88.34   $88.35   $88.30  
  Purchase #4 $228.98   5.463%   $241.4892   $241.49   $241.50   $241.50  
  Purchase #5 $23.52   3.176%   $24.267   $24.27   $24.25   $24.30  
  Purchase #6 $69.45   9.206%   $75.8436   $75.84   $75.85   $75.80  
  Purchase #7 $83.88   7.370%   $90.062   $90.06   $90.05   $90.10  
  7 purchase totals = $730.62       $784.5057   $784.50   $784.50   $784.50