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 $212.73   12.748%   $239.8488   $239.85   $239.85   $239.80  
  Purchase #2 $56.52   4.552%   $59.0928   $59.09   $59.10   $59.10  
  Purchase #3 $12.73   9.404%   $13.9271   $13.93   $13.95   $13.90  
  Purchase #4 $158.88   8.150%   $171.8287   $171.83   $171.85   $171.80  
  Purchase #5 $229.28   6.181%   $243.4518   $243.45   $243.45   $243.50  
  Purchase #6 $71.74   7.499%   $77.1198   $77.12   $77.10   $77.10  
  Purchase #7 $189.51   6.152%   $201.1687   $201.17   $201.15   $201.20  
  7 purchase totals = $931.39       $1,006.4377   $1,006.44   $1,006.45   $1,006.40