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 $238.93   11.123%   $265.5062   $265.51   $265.50   $265.50  
  Purchase #2 $116.26   10.667%   $128.6615   $128.66   $128.65   $128.70  
  Purchase #3 $121.77   13.638%   $138.377   $138.38   $138.40   $138.40  
  Purchase #4 $48.84   5.829%   $51.6869   $51.69   $51.70   $51.70  
  Purchase #5 $178.43   4.836%   $187.0589   $187.06   $187.05   $187.10  
  Purchase #6 $189.58   11.606%   $211.5827   $211.58   $211.60   $211.60  
  Purchase #7 $44.96   12.211%   $50.4501   $50.45   $50.45   $50.50  
  7 purchase totals = $938.77       $1,033.3233   $1,033.33   $1,033.35   $1,033.50