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 $65.26   12.640%   $73.5089   $73.51   $73.50   $73.50  
  Purchase #2 $59.90   6.243%   $63.6396   $63.64   $63.65   $63.60  
  Purchase #3 $158.55   3.488%   $164.0802   $164.08   $164.10   $164.10  
  Purchase #4 $239.32   7.569%   $257.4341   $257.43   $257.45   $257.40  
  Purchase #5 $193.32   12.172%   $216.8509   $216.85   $216.85   $216.90  
  Purchase #6 $163.53   7.403%   $175.6361   $175.64   $175.65   $175.60  
  Purchase #7 $74.74   8.541%   $81.1235   $81.12   $81.10   $81.10  
  7 purchase totals = $954.62       $1,032.2733   $1,032.27   $1,032.30   $1,032.20