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 $114.62   10.839%   $127.0437   $127.04   $127.05   $127.00  
  Purchase #2 $157.77   12.550%   $177.5701   $177.57   $177.55   $177.60  
  Purchase #3 $184.69   10.335%   $203.7777   $203.78   $203.80   $203.80  
  Purchase #4 $31.88   13.831%   $36.2893   $36.29   $36.30   $36.30  
  Purchase #5 $244.26   9.568%   $267.6308   $267.63   $267.65   $267.60  
  Purchase #6 $122.61   10.756%   $135.7979   $135.80   $135.80   $135.80  
  Purchase #7 $221.31   6.841%   $236.4498   $236.45   $236.45   $236.40  
  7 purchase totals = $1,077.14       $1,184.5593   $1,184.56   $1,184.60   $1,184.50