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 $48.28   11.651%   $53.9051   $53.91   $53.90   $53.90  
  Purchase #2 $159.42   4.495%   $166.5859   $166.59   $166.60   $166.60  
  Purchase #3 $234.44   12.868%   $264.6077   $264.61   $264.60   $264.60  
  Purchase #4 $124.71   11.114%   $138.5703   $138.57   $138.55   $138.60  
  Purchase #5 $141.54   13.760%   $161.0159   $161.02   $161.00   $161.00  
  Purchase #6 $9.71   13.246%   $10.9962   $11.00   $11.00   $11.00  
  Purchase #7 $235.73   4.131%   $245.468   $245.47   $245.45   $245.50  
  7 purchase totals = $953.83       $1,041.1491   $1,041.17   $1,041.10   $1,041.20