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 $53.59   12.270%   $60.1655   $60.17   $60.15   $60.20  
  Purchase #2 $245.99   7.297%   $263.9399   $263.94   $263.95   $263.90  
  Purchase #3 $245.54   7.326%   $263.5283   $263.53   $263.55   $263.50  
  Purchase #4 $176.57   12.502%   $198.6448   $198.64   $198.65   $198.60  
  Purchase #5 $191.58   11.234%   $213.1021   $213.10   $213.10   $213.10  
  Purchase #6 $161.72   10.382%   $178.5098   $178.51   $178.50   $178.50  
  Purchase #7 $235.89   13.867%   $268.6009   $268.60   $268.60   $268.60  
  7 purchase totals = $1,310.88       $1,446.4913   $1,446.49   $1,446.50   $1,446.40