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 $32.29   11.125%   $35.8823   $35.88   $35.90   $35.90  
  Purchase #2 $62.67   11.859%   $70.102   $70.10   $70.10   $70.10  
  Purchase #3 $180.36   13.779%   $205.2118   $205.21   $205.20   $205.20  
  Purchase #4 $191.53   5.403%   $201.8784   $201.88   $201.90   $201.90  
  Purchase #5 $165.29   12.591%   $186.1017   $186.10   $186.10   $186.10  
  Purchase #6 $221.64   13.187%   $250.8677   $250.87   $250.85   $250.90  
  Purchase #7 $23.33   11.209%   $25.9451   $25.95   $25.95   $25.90  
  7 purchase totals = $877.11       $975.9890   $975.99   $976.00   $976.00