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 $55.31   11.767%   $61.8183   $61.82   $61.80   $61.80  
  Purchase #2 $124.31   4.524%   $129.9338   $129.93   $129.95   $129.90  
  Purchase #3 $22.51   8.640%   $24.4549   $24.45   $24.45   $24.50  
  Purchase #4 $183.72   11.731%   $205.2722   $205.27   $205.25   $205.30  
  Purchase #5 $135.63   6.466%   $144.3998   $144.40   $144.40   $144.40  
  Purchase #6 $147.93   7.725%   $159.3576   $159.36   $159.35   $159.40  
  Purchase #7 $189.52   6.144%   $201.1641   $201.16   $201.15   $201.20  
  7 purchase totals = $858.93       $926.4007   $926.39   $926.35   $926.50