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 $37.34   3.510%   $38.6506   $38.65   $38.65   $38.70  
  Purchase #2 $201.36   4.302%   $210.0225   $210.02   $210.00   $210.00  
  Purchase #3 $181.38   3.710%   $188.1092   $188.11   $188.10   $188.10  
  Purchase #4 $205.85   5.331%   $216.8239   $216.82   $216.80   $216.80  
  Purchase #5 $60.85   12.212%   $68.281   $68.28   $68.30   $68.30  
  Purchase #6 $173.44   10.661%   $191.9304   $191.93   $191.95   $191.90  
  Purchase #7 $35.36   6.567%   $37.6821   $37.68   $37.70   $37.70  
  7 purchase totals = $895.58       $951.4997   $951.49   $951.50   $951.50