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 $85.28   8.558%   $92.5783   $92.58   $92.60   $92.60  
  Purchase #2 $238.45   7.165%   $255.5349   $255.53   $255.55   $255.50  
  Purchase #3 $162.97   6.771%   $174.0047   $174.00   $174.00   $174.00  
  Purchase #4 $178.32   7.143%   $191.0574   $191.06   $191.05   $191.10  
  Purchase #5 $191.72   8.161%   $207.3663   $207.37   $207.35   $207.40  
  Purchase #6 $164.71   11.779%   $184.1112   $184.11   $184.10   $184.10  
  Purchase #7 $141.93   3.676%   $147.1473   $147.15   $147.15   $147.10  
  7 purchase totals = $1,163.38       $1,251.8001   $1,251.80   $1,251.80   $1,251.80