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 $152.30   9.511%   $166.7853   $166.79   $166.80   $166.80  
  Purchase #2 $243.46   7.863%   $262.6033   $262.60   $262.60   $262.60  
  Purchase #3 $20.50   5.773%   $21.6835   $21.68   $21.70   $21.70  
  Purchase #4 $33.82   4.586%   $35.371   $35.37   $35.35   $35.40  
  Purchase #5 $226.71   6.532%   $241.5187   $241.52   $241.50   $241.50  
  Purchase #6 $189.38   8.835%   $206.1117   $206.11   $206.10   $206.10  
  Purchase #7 $123.49   4.172%   $128.642   $128.64   $128.65   $128.60  
  7 purchase totals = $989.66       $1,062.7155   $1,062.71   $1,062.70   $1,062.70