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 $179.26   12.590%   $201.8288   $201.83   $201.85   $201.80  
  Purchase #2 $250.44   8.869%   $272.6515   $272.65   $272.65   $272.70  
  Purchase #3 $243.97   7.420%   $262.0726   $262.07   $262.05   $262.10  
  Purchase #4 $80.46   7.504%   $86.4977   $86.50   $86.50   $86.50  
  Purchase #5 $5.42   7.372%   $5.8196   $5.82   $5.80   $5.80  
  Purchase #6 $139.98   10.395%   $154.5309   $154.53   $154.55   $154.50  
  Purchase #7 $223.52   11.349%   $248.8873   $248.89   $248.90   $248.90  
  7 purchase totals = $1,123.05       $1,232.2884   $1,232.29   $1,232.30   $1,232.30