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 $71.81   6.195%   $76.2586   $76.26   $76.25   $76.30  
  Purchase #2 $44.81   8.415%   $48.5808   $48.58   $48.60   $48.60  
  Purchase #3 $84.97   4.294%   $88.6186   $88.62   $88.60   $88.60  
  Purchase #4 $157.72   7.535%   $169.6042   $169.60   $169.60   $169.60  
  Purchase #5 $106.55   10.135%   $117.3488   $117.35   $117.35   $117.30  
  Purchase #6 $216.95   8.732%   $235.8941   $235.89   $235.90   $235.90  
  Purchase #7 $216.79   11.270%   $241.2222   $241.22   $241.20   $241.20  
  7 purchase totals = $899.60       $977.5273   $977.52   $977.50   $977.50