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 $228.65   6.854%   $244.3217   $244.32   $244.30   $244.30  
  Purchase #2 $167.58   6.223%   $178.0085   $178.01   $178.00   $178.00  
  Purchase #3 $23.73   9.260%   $25.9274   $25.93   $25.95   $25.90  
  Purchase #4 $55.97   13.323%   $63.4269   $63.43   $63.45   $63.40  
  Purchase #5 $43.28   3.824%   $44.935   $44.94   $44.95   $44.90  
  Purchase #6 $186.64   8.212%   $201.9669   $201.97   $201.95   $202.00  
  Purchase #7 $184.34   3.601%   $190.9781   $190.98   $191.00   $191.00  
  7 purchase totals = $890.19       $949.5645   $949.58   $949.60   $949.50