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 $57.71   9.590%   $63.2444   $63.24   $63.25   $63.20  
  Purchase #2 $63.90   9.591%   $70.0286   $70.03   $70.05   $70.00  
  Purchase #3 $61.87   11.845%   $69.1985   $69.20   $69.20   $69.20  
  Purchase #4 $39.31   6.799%   $41.9827   $41.98   $42.00   $42.00  
  Purchase #5 $74.94   7.701%   $80.7111   $80.71   $80.70   $80.70  
  Purchase #6 $247.53   11.761%   $276.642   $276.64   $276.65   $276.60  
  Purchase #7 $239.95   5.364%   $252.8209   $252.82   $252.80   $252.80  
  7 purchase totals = $785.21       $854.6282   $854.62   $854.65   $854.50