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 $54.80   11.824%   $61.2796   $61.28   $61.30   $61.30  
  Purchase #2 $103.60   13.383%   $117.4648   $117.46   $117.45   $117.50  
  Purchase #3 $52.52   10.668%   $58.1228   $58.12   $58.10   $58.10  
  Purchase #4 $206.83   12.449%   $232.5783   $232.58   $232.60   $232.60  
  Purchase #5 $188.48   9.214%   $205.8465   $205.85   $205.85   $205.80  
  Purchase #6 $213.71   3.142%   $220.4248   $220.42   $220.40   $220.40  
  Purchase #7 $117.72   11.208%   $130.9141   $130.91   $130.90   $130.90  
  7 purchase totals = $937.66       $1,026.6309   $1,026.62   $1,026.60   $1,026.60