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 $209.29   6.694%   $223.2999   $223.30   $223.30   $223.30  
  Purchase #2 $165.88   7.522%   $178.3575   $178.36   $178.35   $178.40  
  Purchase #3 $112.33   8.465%   $121.8387   $121.84   $121.85   $121.80  
  Purchase #4 $63.91   3.723%   $66.2894   $66.29   $66.30   $66.30  
  Purchase #5 $156.51   5.701%   $165.4326   $165.43   $165.45   $165.40  
  Purchase #6 $80.96   7.317%   $86.8838   $86.88   $86.90   $86.90  
  Purchase #7 $202.91   11.322%   $225.8835   $225.88   $225.90   $225.90  
  7 purchase totals = $991.79       $1,067.9854   $1,067.98   $1,068.05   $1,068.00