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 $87.50   5.377%   $92.2049   $92.20   $92.20   $92.20  
  Purchase #2 $86.78   8.146%   $93.8491   $93.85   $93.85   $93.80  
  Purchase #3 $194.77   11.424%   $217.0205   $217.02   $217.00   $217.00  
  Purchase #4 $56.52   7.660%   $60.8494   $60.85   $60.85   $60.80  
  Purchase #5 $181.77   5.691%   $192.1145   $192.11   $192.10   $192.10  
  Purchase #6 $27.73   11.122%   $30.8141   $30.81   $30.80   $30.80  
  Purchase #7 $22.49   9.559%   $24.6398   $24.64   $24.65   $24.60  
  7 purchase totals = $657.56       $711.4923   $711.48   $711.45   $711.30