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 $33.29   13.243%   $37.6986   $37.70   $37.70   $37.70  
  Purchase #2 $207.74   8.319%   $225.0219   $225.02   $225.00   $225.00  
  Purchase #3 $241.93   3.697%   $250.8742   $250.87   $250.85   $250.90  
  Purchase #4 $88.51   11.145%   $98.3744   $98.37   $98.35   $98.40  
  Purchase #5 $183.91   9.330%   $201.0688   $201.07   $201.05   $201.10  
  Purchase #6 $169.26   4.288%   $176.5179   $176.52   $176.50   $176.50  
  Purchase #7 $14.61   7.574%   $15.7166   $15.72   $15.70   $15.70  
  7 purchase totals = $939.25       $1,005.2724   $1,005.27   $1,005.15   $1,005.30