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 $84.92   10.331%   $93.6931   $93.69   $93.70   $93.70  
  Purchase #2 $29.90   12.243%   $33.5607   $33.56   $33.55   $33.60  
  Purchase #3 $142.95   9.317%   $156.2687   $156.27   $156.25   $156.30  
  Purchase #4 $197.51   5.459%   $208.2921   $208.29   $208.30   $208.30  
  Purchase #5 $170.82   10.850%   $189.354   $189.35   $189.35   $189.40  
  Purchase #6 $170.62   4.198%   $177.7826   $177.78   $177.80   $177.80  
  Purchase #7 $227.37   6.278%   $241.6443   $241.64   $241.65   $241.60  
  7 purchase totals = $1,024.09       $1,100.5955   $1,100.58   $1,100.60   $1,100.70