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 $244.44   10.429%   $269.9326   $269.93   $269.95   $269.90  
  Purchase #2 $158.71   5.338%   $167.1819   $167.18   $167.20   $167.20  
  Purchase #3 $191.44   6.560%   $203.9985   $204.00   $204.00   $204.00  
  Purchase #4 $201.46   3.314%   $208.1364   $208.14   $208.15   $208.10  
  Purchase #5 $141.79   5.320%   $149.3332   $149.33   $149.35   $149.30  
  Purchase #6 $48.66   6.855%   $51.9956   $52.00   $52.00   $52.00  
  Purchase #7 $186.79   3.374%   $193.0923   $193.09   $193.10   $193.10  
  7 purchase totals = $1,173.29       $1,243.6705   $1,243.67   $1,243.75   $1,243.60