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 $181.32   6.213%   $192.5854   $192.59   $192.60   $192.60  
  Purchase #2 $62.79   6.627%   $66.9511   $66.95   $66.95   $67.00  
  Purchase #3 $220.28   12.489%   $247.7908   $247.79   $247.80   $247.80  
  Purchase #4 $214.95   9.623%   $235.6346   $235.63   $235.65   $235.60  
  Purchase #5 $156.42   5.768%   $165.4423   $165.44   $165.45   $165.40  
  Purchase #6 $43.70   3.142%   $45.0731   $45.07   $45.05   $45.10  
  Purchase #7 $59.73   9.124%   $65.1798   $65.18   $65.20   $65.20  
  7 purchase totals = $939.19       $1,018.6571   $1,018.65   $1,018.70   $1,018.70