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 $55.46   10.578%   $61.3266   $61.33   $61.35   $61.30  
  Purchase #2 $244.79   8.469%   $265.5213   $265.52   $265.50   $265.50  
  Purchase #3 $11.75   7.164%   $12.5918   $12.59   $12.60   $12.60  
  Purchase #4 $108.98   9.381%   $119.2034   $119.20   $119.20   $119.20  
  Purchase #5 $247.65   8.680%   $269.146   $269.15   $269.15   $269.10  
  Purchase #6 $54.77   9.525%   $59.9868   $59.99   $60.00   $60.00  
  Purchase #7 $55.31   3.599%   $57.3006   $57.30   $57.30   $57.30  
  7 purchase totals = $778.71       $845.0765   $845.08   $845.10   $845.00