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 $224.32   3.524%   $232.225   $232.23   $232.25   $232.20  
  Purchase #2 $93.47   7.623%   $100.5952   $100.60   $100.60   $100.60  
  Purchase #3 $53.93   13.565%   $61.2456   $61.25   $61.25   $61.20  
  Purchase #4 $235.61   13.208%   $266.7294   $266.73   $266.75   $266.70  
  Purchase #5 $235.27   6.156%   $249.7532   $249.75   $249.75   $249.80  
  Purchase #6 $60.67   13.483%   $68.8501   $68.85   $68.85   $68.90  
  Purchase #7 $36.79   8.283%   $39.8373   $39.84   $39.85   $39.80  
  7 purchase totals = $940.06       $1,019.2358   $1,019.25   $1,019.30   $1,019.20