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 $126.83   11.732%   $141.7097   $141.71   $141.70   $141.70  
  Purchase #2 $197.77   3.437%   $204.5674   $204.57   $204.55   $204.60  
  Purchase #3 $177.94   11.477%   $198.3622   $198.36   $198.35   $198.40  
  Purchase #4 $250.44   9.837%   $275.0758   $275.08   $275.10   $275.10  
  Purchase #5 $82.91   12.403%   $93.1933   $93.19   $93.20   $93.20  
  Purchase #6 $36.77   11.416%   $40.9677   $40.97   $40.95   $41.00  
  Purchase #7 $139.91   11.438%   $155.9129   $155.91   $155.90   $155.90  
  7 purchase totals = $1,012.57       $1,109.7890   $1,109.79   $1,109.75   $1,109.90