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 $202.87   11.538%   $226.2771   $226.28   $226.30   $226.30  
  Purchase #2 $232.89   5.356%   $245.3636   $245.36   $245.35   $245.40  
  Purchase #3 $54.99   8.785%   $59.8209   $59.82   $59.80   $59.80  
  Purchase #4 $163.66   7.754%   $176.3502   $176.35   $176.35   $176.40  
  Purchase #5 $19.97   13.256%   $22.6172   $22.62   $22.60   $22.60  
  Purchase #6 $86.85   5.570%   $91.6875   $91.69   $91.70   $91.70  
  Purchase #7 $233.70   3.425%   $241.7042   $241.70   $241.70   $241.70  
  7 purchase totals = $994.93       $1,063.8207   $1,063.82   $1,063.80   $1,063.90