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 $113.37   8.793%   $123.3386   $123.34   $123.35   $123.30  
  Purchase #2 $11.30   12.831%   $12.7499   $12.75   $12.75   $12.70  
  Purchase #3 $38.89   13.347%   $44.0806   $44.08   $44.10   $44.10  
  Purchase #4 $90.69   4.768%   $95.0141   $95.01   $95.00   $95.00  
  Purchase #5 $166.28   12.153%   $186.488   $186.49   $186.50   $186.50  
  Purchase #6 $201.33   5.212%   $211.8233   $211.82   $211.80   $211.80  
  Purchase #7 $110.74   9.752%   $121.5394   $121.54   $121.55   $121.50  
  7 purchase totals = $732.60       $795.0339   $795.03   $795.05   $794.90