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 $52.90   11.738%   $59.1094   $59.11   $59.10   $59.10  
  Purchase #2 $241.74   7.424%   $259.6868   $259.69   $259.70   $259.70  
  Purchase #3 $138.95   5.258%   $146.256   $146.26   $146.25   $146.30  
  Purchase #4 $213.93   12.488%   $240.6456   $240.65   $240.65   $240.60  
  Purchase #5 $10.55   13.632%   $11.9882   $11.99   $12.00   $12.00  
  Purchase #6 $70.55   5.840%   $74.6701   $74.67   $74.65   $74.70  
  Purchase #7 $65.56   6.226%   $69.6418   $69.64   $69.65   $69.60  
  7 purchase totals = $794.18       $861.9979   $862.01   $862.00   $862.00