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 $200.25   6.247%   $212.7596   $212.76   $212.75   $212.80  
  Purchase #2 $170.86   12.677%   $192.5199   $192.52   $192.50   $192.50  
  Purchase #3 $85.81   9.387%   $93.865   $93.87   $93.85   $93.90  
  Purchase #4 $146.65   7.112%   $157.0797   $157.08   $157.10   $157.10  
  Purchase #5 $211.32   7.329%   $226.8076   $226.81   $226.80   $226.80  
  Purchase #6 $43.77   7.643%   $47.1153   $47.12   $47.10   $47.10  
  Purchase #7 $45.75   4.837%   $47.9629   $47.96   $47.95   $48.00  
  7 purchase totals = $904.41       $978.1100   $978.12   $978.05   $978.20