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 $61.93   8.288%   $67.0628   $67.06   $67.05   $67.10  
  Purchase #2 $233.87   3.270%   $241.5175   $241.52   $241.50   $241.50  
  Purchase #3 $9.45   7.805%   $10.1876   $10.19   $10.20   $10.20  
  Purchase #4 $81.94   3.827%   $85.0758   $85.08   $85.10   $85.10  
  Purchase #5 $55.76   11.599%   $62.2276   $62.23   $62.25   $62.20  
  Purchase #6 $208.98   7.344%   $224.3275   $224.33   $224.35   $224.30  
  Purchase #7 $55.29   6.622%   $58.9513   $58.95   $58.95   $59.00  
  7 purchase totals = $707.22       $749.3501   $749.36   $749.40   $749.40