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 $213.85   4.538%   $223.5545   $223.55   $223.55   $223.60  
  Purchase #2 $216.39   3.653%   $224.2947   $224.29   $224.30   $224.30  
  Purchase #3 $151.30   10.313%   $166.9036   $166.90   $166.90   $166.90  
  Purchase #4 $68.68   7.218%   $73.6373   $73.64   $73.65   $73.60  
  Purchase #5 $196.74   11.217%   $218.8083   $218.81   $218.80   $218.80  
  Purchase #6 $179.30   11.668%   $200.2207   $200.22   $200.20   $200.20  
  Purchase #7 $114.42   10.766%   $126.7385   $126.74   $126.75   $126.70  
  7 purchase totals = $1,140.68       $1,234.1576   $1,234.15   $1,234.15   $1,234.10