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 $60.60   7.791%   $65.3213   $65.32   $65.30   $65.30  
  Purchase #2 $134.95   9.345%   $147.5611   $147.56   $147.55   $147.60  
  Purchase #3 $196.36   13.460%   $222.7901   $222.79   $222.80   $222.80  
  Purchase #4 $234.81   7.362%   $252.0967   $252.10   $252.10   $252.10  
  Purchase #5 $58.26   6.397%   $61.9869   $61.99   $62.00   $62.00  
  Purchase #6 $104.53   10.589%   $115.5987   $115.60   $115.60   $115.60  
  Purchase #7 $138.90   6.371%   $147.7493   $147.75   $147.75   $147.70  
  7 purchase totals = $928.41       $1,013.1041   $1,013.11   $1,013.10   $1,013.10