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 $62.29   9.560%   $68.2449   $68.24   $68.25   $68.20  
  Purchase #2 $119.34   3.779%   $123.8499   $123.85   $123.85   $123.80  
  Purchase #3 $125.36   12.547%   $141.0889   $141.09   $141.10   $141.10  
  Purchase #4 $63.72   6.631%   $67.9453   $67.95   $67.95   $67.90  
  Purchase #5 $228.39   6.575%   $243.4066   $243.41   $243.40   $243.40  
  Purchase #6 $232.36   12.238%   $260.7962   $260.80   $260.80   $260.80  
  Purchase #7 $73.99   13.512%   $83.9875   $83.99   $84.00   $84.00  
  7 purchase totals = $905.45       $989.3193   $989.33   $989.35   $989.20