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 $134.41   13.298%   $152.2838   $152.28   $152.30   $152.30  
  Purchase #2 $127.81   9.673%   $140.1731   $140.17   $140.15   $140.20  
  Purchase #3 $80.88   6.720%   $86.3151   $86.32   $86.30   $86.30  
  Purchase #4 $197.41   3.827%   $204.9649   $204.96   $204.95   $205.00  
  Purchase #5 $101.35   6.299%   $107.734   $107.73   $107.75   $107.70  
  Purchase #6 $198.81   5.520%   $209.7843   $209.78   $209.80   $209.80  
  Purchase #7 $150.52   5.299%   $158.4961   $158.50   $158.50   $158.50  
  7 purchase totals = $991.19       $1,059.7513   $1,059.74   $1,059.75   $1,059.80