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 $211.73   9.581%   $232.0159   $232.02   $232.00   $232.00  
  Purchase #2 $99.36   4.118%   $103.4516   $103.45   $103.45   $103.50  
  Purchase #3 $155.69   9.108%   $169.8702   $169.87   $169.85   $169.90  
  Purchase #4 $111.37   3.527%   $115.298   $115.30   $115.30   $115.30  
  Purchase #5 $165.61   7.472%   $177.9844   $177.98   $178.00   $178.00  
  Purchase #6 $169.95   8.476%   $184.355   $184.36   $184.35   $184.40  
  Purchase #7 $68.66   10.122%   $75.6098   $75.61   $75.60   $75.60  
  7 purchase totals = $982.37       $1,058.5849   $1,058.59   $1,058.55   $1,058.70