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 $225.76   11.109%   $250.8397   $250.84   $250.85   $250.80  
  Purchase #2 $198.39   5.773%   $209.8431   $209.84   $209.85   $209.80  
  Purchase #3 $65.47   12.239%   $73.4829   $73.48   $73.50   $73.50  
  Purchase #4 $111.99   7.585%   $120.4844   $120.48   $120.50   $120.50  
  Purchase #5 $22.58   13.666%   $25.6658   $25.67   $25.65   $25.70  
  Purchase #6 $163.87   6.562%   $174.6231   $174.62   $174.60   $174.60  
  Purchase #7 $229.32   6.172%   $243.4736   $243.47   $243.45   $243.50  
  7 purchase totals = $1,017.38       $1,098.4126   $1,098.40   $1,098.40   $1,098.40