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 $46.71   7.774%   $50.3412   $50.34   $50.35   $50.30  
  Purchase #2 $71.86   8.270%   $77.8028   $77.80   $77.80   $77.80  
  Purchase #3 $204.31   6.560%   $217.7127   $217.71   $217.70   $217.70  
  Purchase #4 $94.41   7.334%   $101.334   $101.33   $101.35   $101.30  
  Purchase #5 $209.66   9.441%   $229.454   $229.45   $229.45   $229.50  
  Purchase #6 $175.59   13.613%   $199.4931   $199.49   $199.50   $199.50  
  Purchase #7 $216.54   12.443%   $243.4841   $243.48   $243.50   $243.50  
  7 purchase totals = $1,019.08       $1,119.6219   $1,119.60   $1,119.65   $1,119.60