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 $227.37   9.796%   $249.6432   $249.64   $249.65   $249.60  
  Purchase #2 $168.92   11.438%   $188.2411   $188.24   $188.25   $188.20  
  Purchase #3 $94.57   4.337%   $98.6715   $98.67   $98.65   $98.70  
  Purchase #4 $102.53   8.439%   $111.1825   $111.18   $111.20   $111.20  
  Purchase #5 $119.60   9.128%   $130.5171   $130.52   $130.50   $130.50  
  Purchase #6 $145.65   10.813%   $161.3991   $161.40   $161.40   $161.40  
  Purchase #7 $78.92   10.644%   $87.3202   $87.32   $87.30   $87.30  
  7 purchase totals = $937.56       $1,026.9747   $1,026.97   $1,026.95   $1,026.90