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 $209.59   4.124%   $218.2335   $218.23   $218.25   $218.20  
  Purchase #2 $236.97   4.647%   $247.982   $247.98   $248.00   $248.00  
  Purchase #3 $63.61   6.230%   $67.5729   $67.57   $67.55   $67.60  
  Purchase #4 $197.71   9.686%   $216.8602   $216.86   $216.85   $216.90  
  Purchase #5 $96.90   7.581%   $104.246   $104.25   $104.25   $104.20  
  Purchase #6 $147.93   7.714%   $159.3413   $159.34   $159.35   $159.30  
  Purchase #7 $160.78   6.686%   $171.5298   $171.53   $171.55   $171.50  
  7 purchase totals = $1,113.49       $1,185.7657   $1,185.76   $1,185.80   $1,185.70