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 $95.29   10.782%   $105.5642   $105.56   $105.55   $105.60  
  Purchase #2 $134.29   13.326%   $152.1855   $152.19   $152.20   $152.20  
  Purchase #3 $219.48   12.323%   $246.5265   $246.53   $246.55   $246.50  
  Purchase #4 $164.97   7.613%   $177.5292   $177.53   $177.55   $177.50  
  Purchase #5 $139.64   3.209%   $144.121   $144.12   $144.10   $144.10  
  Purchase #6 $8.75   12.269%   $9.8235   $9.82   $9.80   $9.80  
  Purchase #7 $230.28   6.553%   $245.3702   $245.37   $245.35   $245.40  
  7 purchase totals = $992.70       $1,081.1201   $1,081.12   $1,081.10   $1,081.10