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 $119.64   12.126%   $134.1475   $134.15   $134.15   $134.10  
  Purchase #2 $8.27   12.703%   $9.3205   $9.32   $9.30   $9.30  
  Purchase #3 $198.52   7.181%   $212.7757   $212.78   $212.80   $212.80  
  Purchase #4 $232.34   4.594%   $243.0137   $243.01   $243.00   $243.00  
  Purchase #5 $206.32   12.528%   $232.1678   $232.17   $232.15   $232.20  
  Purchase #6 $48.68   10.216%   $53.6531   $53.65   $53.65   $53.70  
  Purchase #7 $102.40   6.392%   $108.9454   $108.95   $108.95   $108.90  
  7 purchase totals = $916.17       $994.0237   $994.03   $994.00   $994.00