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 $60.89   8.123%   $65.8361   $65.84   $65.85   $65.80  
  Purchase #2 $148.95   5.365%   $156.9412   $156.94   $156.95   $156.90  
  Purchase #3 $134.88   6.311%   $143.3923   $143.39   $143.40   $143.40  
  Purchase #4 $220.28   13.843%   $250.7734   $250.77   $250.75   $250.80  
  Purchase #5 $113.69   5.675%   $120.1419   $120.14   $120.15   $120.10  
  Purchase #6 $147.80   6.197%   $156.9592   $156.96   $156.95   $157.00  
  Purchase #7 $99.37   7.368%   $106.6916   $106.69   $106.70   $106.70  
  7 purchase totals = $925.86       $1,000.7357   $1,000.73   $1,000.75   $1,000.70