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 $43.58   12.287%   $48.9347   $48.93   $48.95   $48.90  
  Purchase #2 $160.87   9.139%   $175.5719   $175.57   $175.55   $175.60  
  Purchase #3 $156.68   13.394%   $177.6657   $177.67   $177.65   $177.70  
  Purchase #4 $172.46   11.336%   $192.0101   $192.01   $192.00   $192.00  
  Purchase #5 $53.36   11.272%   $59.3747   $59.37   $59.35   $59.40  
  Purchase #6 $82.45   5.485%   $86.9724   $86.97   $86.95   $87.00  
  Purchase #7 $228.89   6.568%   $243.9235   $243.92   $243.90   $243.90  
  7 purchase totals = $898.29       $984.4530   $984.44   $984.35   $984.50