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 $216.32   13.499%   $245.521   $245.52   $245.50   $245.50  
  Purchase #2 $25.86   12.216%   $29.0191   $29.02   $29.00   $29.00  
  Purchase #3 $11.80   12.501%   $13.2751   $13.28   $13.30   $13.30  
  Purchase #4 $62.35   4.688%   $65.273   $65.27   $65.25   $65.30  
  Purchase #5 $134.88   12.239%   $151.388   $151.39   $151.40   $151.40  
  Purchase #6 $250.66   8.731%   $272.5451   $272.55   $272.55   $272.50  
  Purchase #7 $241.80   4.547%   $252.7946   $252.79   $252.80   $252.80  
  7 purchase totals = $943.67       $1,029.8159   $1,029.82   $1,029.80   $1,029.80