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 $58.50   12.280%   $65.6838   $65.68   $65.70   $65.70  
  Purchase #2 $68.72   8.238%   $74.3812   $74.38   $74.40   $74.40  
  Purchase #3 $177.80   6.605%   $189.5437   $189.54   $189.55   $189.50  
  Purchase #4 $102.49   12.320%   $115.1168   $115.12   $115.10   $115.10  
  Purchase #5 $209.90   3.235%   $216.6903   $216.69   $216.70   $216.70  
  Purchase #6 $216.32   6.418%   $230.2034   $230.20   $230.20   $230.20  
  Purchase #7 $43.37   12.835%   $48.9365   $48.94   $48.95   $48.90  
  7 purchase totals = $877.10       $940.5557   $940.55   $940.60   $940.50