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 $58.89   6.470%   $62.7002   $62.70   $62.70   $62.70  
  Purchase #2 $182.54   4.737%   $191.1869   $191.19   $191.20   $191.20  
  Purchase #3 $142.72   9.323%   $156.0258   $156.03   $156.05   $156.00  
  Purchase #4 $191.85   11.639%   $214.1794   $214.18   $214.20   $214.20  
  Purchase #5 $101.67   11.229%   $113.0865   $113.09   $113.10   $113.10  
  Purchase #6 $44.97   7.418%   $48.3059   $48.31   $48.30   $48.30  
  Purchase #7 $235.25   13.201%   $266.3054   $266.31   $266.30   $266.30  
  7 purchase totals = $957.89       $1,051.7901   $1,051.81   $1,051.85   $1,051.80