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 $114.77   10.759%   $127.1181   $127.12   $127.10   $127.10  
  Purchase #2 $39.37   13.135%   $44.5412   $44.54   $44.55   $44.50  
  Purchase #3 $225.26   5.121%   $236.7956   $236.80   $236.80   $236.80  
  Purchase #4 $120.27   11.644%   $134.2742   $134.27   $134.25   $134.30  
  Purchase #5 $93.99   10.654%   $104.0037   $104.00   $104.00   $104.00  
  Purchase #6 $217.51   7.717%   $234.2952   $234.30   $234.30   $234.30  
  Purchase #7 $58.86   8.411%   $63.8107   $63.81   $63.80   $63.80  
  7 purchase totals = $870.03       $944.8387   $944.84   $944.80   $944.80