Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $126.51   6.282%   $134.4574   $134.46   $134.45   $134.50  
  Purchase #2 $61.35   12.145%   $68.801   $68.80   $68.80   $68.80  
  Purchase #3 $97.30   9.522%   $106.5649   $106.56   $106.55   $106.60  
  Purchase #4 $181.25   10.366%   $200.0384   $200.04   $200.05   $200.00  
  Purchase #5 $246.40   13.117%   $278.7203   $278.72   $278.70   $278.70  
  Purchase #6 $28.87   6.219%   $30.6654   $30.67   $30.65   $30.70  
  Purchase #7 $234.30   4.136%   $243.9906   $243.99   $244.00   $244.00  
  7 purchase totals = $975.98       $1,063.2380   $1,063.24   $1,063.20   $1,063.30