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 $55.86   12.743%   $62.9782   $62.98   $63.00   $63.00  
  Purchase #2 $143.46   12.705%   $161.6866   $161.69   $161.70   $161.70  
  Purchase #3 $241.25   5.215%   $253.8312   $253.83   $253.85   $253.80  
  Purchase #4 $202.91   12.268%   $227.803   $227.80   $227.80   $227.80  
  Purchase #5 $49.81   11.242%   $55.4096   $55.41   $55.40   $55.40  
  Purchase #6 $143.88   4.148%   $149.8481   $149.85   $149.85   $149.80  
  Purchase #7 $25.67   12.585%   $28.9006   $28.90   $28.90   $28.90  
  7 purchase totals = $862.84       $940.4573   $940.46   $940.50   $940.40