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 $204.35   9.381%   $223.5201   $223.52   $223.50   $223.50  
  Purchase #2 $225.92   10.470%   $249.5738   $249.57   $249.55   $249.60  
  Purchase #3 $88.79   8.867%   $96.663   $96.66   $96.65   $96.70  
  Purchase #4 $232.27   10.766%   $257.2762   $257.28   $257.30   $257.30  
  Purchase #5 $88.33   8.590%   $95.9175   $95.92   $95.90   $95.90  
  Purchase #6 $77.69   4.712%   $81.3508   $81.35   $81.35   $81.40  
  Purchase #7 $224.65   10.788%   $248.8852   $248.89   $248.90   $248.90  
  7 purchase totals = $1,142.00       $1,253.1866   $1,253.19   $1,253.15   $1,253.30