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 $65.25   12.372%   $73.3227   $73.32   $73.30   $73.30  
  Purchase #2 $139.93   7.164%   $149.9546   $149.95   $149.95   $150.00  
  Purchase #3 $103.66   5.408%   $109.2659   $109.27   $109.25   $109.30  
  Purchase #4 $198.66   8.362%   $215.2719   $215.27   $215.25   $215.30  
  Purchase #5 $69.57   10.190%   $76.6592   $76.66   $76.65   $76.70  
  Purchase #6 $7.94   7.337%   $8.5226   $8.52   $8.50   $8.50  
  Purchase #7 $219.25   4.746%   $229.6556   $229.66   $229.65   $229.70  
  7 purchase totals = $804.26       $862.6525   $862.65   $862.55   $862.80