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 $68.82   12.837%   $77.6544   $77.65   $77.65   $77.70  
  Purchase #2 $175.97   5.795%   $186.1675   $186.17   $186.15   $186.20  
  Purchase #3 $56.77   4.578%   $59.3689   $59.37   $59.35   $59.40  
  Purchase #4 $207.60   5.811%   $219.6636   $219.66   $219.65   $219.70  
  Purchase #5 $129.79   9.428%   $142.0266   $142.03   $142.05   $142.00  
  Purchase #6 $195.64   9.592%   $214.4058   $214.41   $214.40   $214.40  
  Purchase #7 $58.69   6.311%   $62.3939   $62.39   $62.40   $62.40  
  7 purchase totals = $893.28       $961.6807   $961.68   $961.65   $961.80