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 $46.59   6.850%   $49.7814   $49.78   $49.80   $49.80  
  Purchase #2 $181.78   3.865%   $188.8058   $188.81   $188.80   $188.80  
  Purchase #3 $31.26   13.455%   $35.466   $35.47   $35.45   $35.50  
  Purchase #4 $193.33   12.286%   $217.0825   $217.08   $217.10   $217.10  
  Purchase #5 $244.33   3.765%   $253.529   $253.53   $253.55   $253.50  
  Purchase #6 $207.79   9.211%   $226.9295   $226.93   $226.95   $226.90  
  Purchase #7 $54.36   10.365%   $59.9944   $59.99   $60.00   $60.00  
  7 purchase totals = $959.44       $1,031.5886   $1,031.59   $1,031.65   $1,031.60