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 $193.80   6.154%   $205.7265   $205.73   $205.75   $205.70  
  Purchase #2 $146.93   5.674%   $155.2668   $155.27   $155.25   $155.30  
  Purchase #3 $239.64   13.802%   $272.7151   $272.72   $272.70   $272.70  
  Purchase #4 $243.56   13.671%   $276.8571   $276.86   $276.85   $276.90  
  Purchase #5 $11.85   6.837%   $12.6602   $12.66   $12.65   $12.70  
  Purchase #6 $239.56   11.395%   $266.8579   $266.86   $266.85   $266.90  
  Purchase #7 $185.40   8.654%   $201.4445   $201.44   $201.45   $201.40  
  7 purchase totals = $1,260.74       $1,391.5281   $1,391.54   $1,391.50   $1,391.60