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 $46.39   13.551%   $52.6763   $52.68   $52.70   $52.70  
  Purchase #2 $82.65   8.846%   $89.9612   $89.96   $89.95   $90.00  
  Purchase #3 $68.59   12.547%   $77.196   $77.20   $77.20   $77.20  
  Purchase #4 $178.34   11.570%   $198.9739   $198.97   $198.95   $199.00  
  Purchase #5 $198.38   10.730%   $219.6662   $219.67   $219.65   $219.70  
  Purchase #6 $56.89   8.335%   $61.6318   $61.63   $61.65   $61.60  
  Purchase #7 $96.52   10.805%   $106.949   $106.95   $106.95   $106.90  
  7 purchase totals = $727.76       $807.0544   $807.06   $807.05   $807.10